Multicenter Phase I Trial of a DNA Vaccine Encoding the Androgen Receptor Ligand-binding Domain (pTVG-AR, MVI-118) in Patients with Metastatic Prostate Cancer

This article is featured in Highlights of This Issue, p. 5053

Prostate cancer remains a leading cause of cancer-related death worldwide (1). While nearly two-third of patients with organ-confined disease will be cured with definitive surgery or radiotherapy, approximately one-third will have recurrence. Prostate cancer, once metastatic, is not curable, and is generally initially treated with androgen ablation therapy. Median survival for patients with metastatic prostate cancer is approximately 5 years; however, recent trials have demonstrated that the addition of docetaxel or androgen-targeted agents, such as abiraterone, enzalutamide, or apalutamide, can prolong survival in patients with metastatic prostate cancer beginning androgen deprivation therapy (ADT; refs. 2–5). Metastatic prostate cancer that develops resistance to surgical or medical castration represents the lethal form of the disease. While several agents have been shown to prolong survival of men with castration-resistant prostate cancer (CRPC), the median survival benefit of each drug is only on the order of a few months (6–10). Consequently, there is an urgent need to identify treatments able to prevent the establishment of metastatic disease and/or to prolong the period of response to androgen deprivation prior to the development of lethal CRPC.

Cancer vaccines aim to eliminate or slow tumor growth by expanding and activating tumor-specific T cells. Sipuleucel-T, an antigen-presenting cell cancer vaccine, was approved by FDA as a treatment for metastatic CRPC following trials showing prolonged survival, providing proof-of-concept for the use of cancer vaccines in treating prostate cancer (11). To build on this approach, we have sought to identify other tumor-associated antigenic targets and optimize vaccine methods. In preclinical studies, we have focused on identifying immunologically recognizable proteins, shared among multiple patients, that might serve as vaccine antigens, and on cost-effective vaccine methods that can elicit immunity to these antigens. We hypothesized that the androgen receptor (AR) might be an ideal target antigen, as it is the core oncogenic driver of prostate cancer, and has been the primary treatment target of hormone-sensitive disease for over 50 years (12). Moreover, we reasoned that T cells specific for the AR, augmented by vaccination, might better target castration-resistant tumors that overexpress AR as a mechanism of resistance to androgen deprivation. In support of our hypothesis, we have previously reported that some patients with prostate cancer, compared with men without prostate cancer, have antibody and CD8⁺ T-cell immunity to the AR, suggesting that immune responses to the AR can arise with the development of prostate cancer (13, 14).

In preclinical models, we have evaluated a DNA vaccine encoding the ligand-binding domain (LBD) of the AR (pTVG-AR, MVI-118), given that the sequence of this domain is identical among multiple species, including mice, rats, and humans. We found that vaccination of male, immunocompetent mice could elicit AR-specific CD8⁺ T cells with cytolytic function, which delayed the establishment of tumors in transgenic mice, and prolonged the survival of prostate tumor-bearing mice or rats (15). Treatment was not associated with adverse effects on normal tissues (16). Finally, we found that androgen deprivation of prostate tumor cells led to increased expression of the AR, making tumor cells more susceptible to lysis by AR-specific CD8⁺ T cells, and that AR-targeted vaccination combined with androgen deprivation led to a delay in the development of castration-resistant tumors in mice (17). Given these findings, we hypothesized that patients with newly metastatic prostate cancer beginning androgen deprivation would be the ideal population in which to evaluate this vaccine, with the ultimate clinical goal of targeting AR overexpression as a mechanism of resistance, and hence prolonging or avoiding the development of castration resistance. We report here the results from a multicenter first-in-human phase I clinical trial using this same DNA vaccine in patients with metastatic castration-sensitive prostate cancer (mCSPC).

pTVG-AR (MVI-118) is a plasmid DNA encoding the LBD of the human androgen receptor (AR LBD) cDNA downstream of a eukaryotic promoter (15). The study protocol was reviewed and approved by all local and federal entities (FDA, NIH Recombinant DNA Advisory Committee), as well as the institutional review board at each participating site. The study was conducted according to the provisions of the Declaration of Helsinki and Good Clinical Practice Guidelines of the International Council on Harmonization. All patients provided written informed consent before participating.

Male patients with adenocarcinoma of the prostate and evidence of metastatic disease by CT, MRI, and/or bone scintigraphy were eligible. Patients were required to have started standard ADT [bilateral orchiectomy or luteinizing hormone-releasing hormone (LHRH) agonist, and with or without an androgen antagonist] within 6 months of study entry, with evidence of PSA decline on treatment, and have castrate levels of testosterone. Patients were not allowed to change the type of ADT used while on treatment, and were required to continue ADT throughout the study treatment period. Patients who were deemed candidates for docetaxel chemotherapy were not eligible, and this study was conducted before other agents (e.g., abiraterone or enzalutamide) were approved for use in this disease stage. Patients were further required to have an Eastern Cooperative Oncology Group performance score ≤1, and normal bone marrow, liver, and renal function.

This was an open-label, randomized, multi-institutional phase I trial designed to evaluate two different schedules of pTVG-AR administration with or without GM-CSF used as a vaccine adjuvant. The primary objectives were safety and immune response to pTVG-AR. Secondary objectives were to evaluate the impact of different schedules of pTVG-AR and GM-CSF on immune response, and to determine median time to PSA progression and 18-month PPFS while receiving ADT. The proposed sample size of 40 patients, 10 patients per study arm, was chosen to detect toxicity incidences given that the probability of observing at least one incidence of grade ≥ 3 toxicity in 10 patients was >95%, assuming a true toxicity rate of 33%. This sample size was also adequate for identifying the arm with the highest immune response rate with a high probability (selection design with >80% power) so that the results of the trial could be used to prioritize a possible preferred schedule of administration for subsequent trials.

Patients were randomized to one of four treatment arms (Fig. 1A). In Arms 1 and 3, patients received six intradermal injections at 14-day intervals, and then quarterly for up to 12 months (10 total vaccinations), with 100-μg pTVG-AR plasmid DNA, and with (Arm 3) or without (Arm 1) 200-μg GM-CSF (Leukine, sargramostim) admixed with the DNA (Fig. 1B). In Arms 2 and 4, patients received two intradermal injections 14 days apart with 100-μg pTVG-AR as a treatment cycle that was repeated every 12 weeks over one year (10 total vaccinations), and were again given with (Arm 4) or without (Arm 2) 200-μg GM-CSF admixed with the DNA (Fig. 1B). All subjects were immunized with tetanus toxoid prior to receiving study treatment, as a positive immunologic control, and immune responses were similarly evaluated to tetanus toxoid and PSA, as a tumor-specific nontargeted antigen. Safety labs were performed monthly for the first 3 months, and then quarterly. Serum PSA was obtained monthly throughout the 18-month study period. Patients underwent leukapheresis of up to 100-mL volume prior to treatment and at one year, and had additional quarterly blood collections, for immunologic analyses. All toxicities were graded using NCI CTCAE, version 4. Radiographic imaging was not scheduled as per protocol but permitted at any time as per physician discretion. Patients were to come off trial at the time of PSA progression [defined as a serum PSA value at least 25% over the nadir, an absolute increase of 2 ng/mL over the nadir, and verified by repeat value at least 3 weeks later (18, 19)], radiographic disease progression, if undue toxicity, or at the discretion of the patient or physician that other therapies were warranted.

Antigen-specific T cells secreting IFNγ or granzyme B were detected by ELISpot, using methods as reported previously (20, 21). This analysis was performed from 30 patients treated at one clinical site, with analysis performed for each sample in real time, without cryopreservation of samples. All antigens and sera used were from the same lots to control for possible variation over time. Test antigens included phytohemaglutinin (positive control), media alone, tetanus toxoid (EMD Millipore), and pools of 15-mer peptides spanning the amino acid sequence of either PSA (as a tumor-specific, nontargeted antigen) or the AR LBD, with adjacent peptides in each pool overlapping by 11 amino acids (LifeTein, LLC). A response resulting from immunization was defined as an antigen-specific response detectable more than once posttreatment that was both significant (compared with media only control), at least 3-fold higher than the pretreatment value, and with a frequency > 10 spot-forming units (SFU) per million peripheral blood mononuclear cell (PBMC). Immune responses over time were evaluated as an AUC, using antigen-specific SFU at each time point following subtraction of the pretreatment value (GraphPad Prism, version 5).

IgG antibody responses to tetanus, PSA, and the AR LBD were evaluated by Luminex. Beads coated with AR LBD protein (Invitrogen), PSA protein (Fitzgerald Industries International), or tetanus toxoid (EMD Millipore) were prepared as per manufacturer's recommendations (xMAP antibody coupling kit and MagPlex microspheres, Luminex). Serum samples were diluted 1:100 in PBS/1% BSA, and incubated overnight at 4°C with the beads in wells of a 96-well plate. Plates were washed multiple times, IgG detected with biotinylated secondary antibody and avidin-fluorophore, and quantified by Luminex MAGPIX. Results are displayed as change in response from baseline over time.

Time to treatment failure was evaluated from the start of study treatment and also from the start of ADT prior to study enrollment. Treatment failure was defined as the first evidence of castration resistance (PSA at least 25% over the nadir, an absolute increase of 2 ng/mL over the nadir, and verified by repeat value at least 3 weeks later), at which point patients came off study. The time to the first rise in PSA at least 0.1 ng/mL over the nadir, verified by repeat value at least 3 weeks later, was also evaluated as a separate measure of early treatment failure, but not requiring study discontinuation. If there was no PSA progression event, then time to treatment failure was censored at the last available PSA assessment.

Baseline characteristics were summarized by frequencies and percentages or medians and ranges. Toxicity rates were compared between groups using Fisher exact test. Time-to-treatment failure/PSA progression was analyzed using the Kaplan–Meier method and compared between arms using the unstratified log-rank test and univariate Cox proportional hazard model. Analogously, changes in immune response parameters between arms were evaluated using a nonparametric Wilcoxon rank-sum test. All reported P values are two-sided and P < 0.05 was used to define statistical significance. Statistical analyses were conducted using SAS software (SAS Institute Inc.), version 9.4.

Forty patients were enrolled between August 2015 and November 2017 at the University of Wisconsin—Madison (Madison, WI), Rutgers Cancer Institute of New Jersey, and the University of Washington (Seattle, WA; Fig. 1A; Table 1). The median age of participants was 69 years (range, 51–84 years). Twenty-seven subjects (68%) completed treatment without progression at 18 months. Eleven patients (28%) came off study due to rising PSA, two of which did not meet study criteria for PSA or radiographic progression. Two additional patients ended treatment early, one due to a secondary cancer diagnosis, and the other due to experiencing grade 2 heart failure. The heart failure was believed to be at least possibly treatment related.

A total of 79 treatment-related adverse events were observed over the period of study (10 for Arm 1, 11 for Arm 2, 23 for Arm 3, and 35 for Arm 4). No grade 3 or 4 events deemed at least possibly related to study treatment were observed. The most common grade 1 and 2 adverse events were fatigue, chills, arthralgias, and injection site reactions. Injection site reactions were more common in the groups receiving GM-CSF adjuvant (62% vs. 16%; P = 0.008). Otherwise, adverse events were not significantly different among the treatment arms (Table 2).

ELISPOT was used to identify AR LBD–specific T cells secreting IFNγ or granzyme B. As shown in Fig. 2A, AR LBD–specific IFNγ-secreting T cells, in frequencies at least 3-fold higher than baseline, were detected at least twice in follow-up in 9/30 (30%) patients. AR LBD–specific granzyme B-secreting T cells, in frequency at least 3-fold higher than baseline, were detected at least twice in follow-up in 12/30 (40%) patients (Fig. 2B). AR LBD–specific T cells secreting IFNγ or granzyme B were detected in 16/30 (53%) patients.

As also shown in Fig. 2, tetanus-specific T cells, secreting granzyme B or IFNγ, were detected in 13/30 (43%) patients. PSA-specific T cells, secreting granzyme B or IFNγ, were detected in 9/30 (30%) patients. Of note, PSA-specific T-cell responses were only detected in patients with immune response to the AR LBD, whereas 4/13 (31%) patients with response to tetanus did not have response to AR LBD, and 2/9 (22%) of patients with response to PSA did not have response to tetanus.

To evaluate differences in immune response due to vaccine schedule and/or the use of GM-CSF adjuvant, the magnitude of response to AR LBD, as detected by IFNγ ELISPOT, was evaluated over time compared with the baseline measurement. As shown in Fig. 3A, immune responses to AR LBD were generally of greater magnitude in patients treated in Arms 1 and 3 (same schedule, with or without GM-CSF), and tended to increase over the first several immunizations. The durability of immunity was assessed by evaluating these data over time as an AUC. As shown in Fig. 3B, immune responses to AR LBD were significantly more durable over time in these same treatment arms. No significant differences were observed in magnitude or durability of immune response in patients who received GM-CSF adjuvant compared with those that did not. IFNγ-secreting immune responses to tetanus toxoid were similar among all treatment arms (Supplementary Fig. S1). Immune responses to PSA were generally lower in magnitude, and mostly detectable in patients treated with the schedule of Arms 1 and 3 (Supplementary Fig. S2).

IgG serum antibody responses to AR LBD, PSA, and tetanus toxoid were evaluated over time for all 40 patients by Luminex assay. IgG responses to tetanus toxoid increased in the majority of patients. Antibody responses to AR LBD and PSA; however, did not significantly change over time (Supplementary Fig. S3).

Twenty-seven out of 40 (68%) patients were progression-free at 18 months. The median time to first PSA rise was 9.2 months from start of study treatment, and 11.7 months from starting ADT prior to study treatment. As shown in Fig. 4A, the time to castration resistance or first PSA rise was not significantly different among study arms grouped with respect to use of GM-CSF adjuvant or not. However, as shown in Fig. 4B, the time to first PSA rise was significantly longer (median time: 13.8 vs. 4.6 months; HR = 0.42; CI, 0.19–0.92; P = 0.02) in patients treated with the schedule of Arms 2 and 4 compared with the other treatment schedule. As shown in Fig. 4C, patients who developed IFNγ and/or granzyme B immunity to the AR LBD had a significantly prolonged time to castration resistance (median time: not reached vs. 9.2 months; HR 0.01; 95% CI, 0–0.021; P = 0.003) or first PSA rise (median time: 12.5 vs. 4.6 months; HR 0.18; 95% CI, 0.05–0.64; P = 0.008). There was no significant association observed between immunity to tetanus or PSA and time to castration resistance or time to first PSA rise (data not shown).

In preclinical models, we previously demonstrated that androgen deprivation leads to an increase in expression of AR, which in turn can make prostate cancer cells more recognizable by CD8⁺ T cells specific for the AR (17). Vaccination targeting AR led to an increase in time to progression when combined with androgen deprivation in murine prostate cancer models (17). In this phase I study, we have evaluated the same DNA vaccine encoding the AR LBD in men with mCSPC. We found that: (i) vaccination with pTVG-AR (MVI-118) was safe; (ii) vaccination elicited a T-cell response to the AR LBD in the majority of patients; (iii) a preferred schedule of immunization was identified that led to greater magnitude and durability of Th1-type immunity; (iv) the use of GM-CSF adjuvant did not substantially affect the development of immune response to the target antigen; (v) vaccination elicited immunity to a nontargeted tumor antigen (PSA) consistent with “antigen spread;” and (vi) immune response to AR LBD augmented with immunization was associated with a longer time to castration resistance, and early PSA rise preceding the onset of castration resistance.

Vaccination with pTVG-AR was safe and well tolerated. We observed that injection site reactions were more common in patients receiving GM-CSF adjuvant, suggesting these were mostly due to GM-CSF. The absence of significant toxicity is notable because the AR-targeted antigen is also expressed in normal tissues (e.g., muscle, liver, and skin; ref. 22). No toxicity was observed in these tissues. This was not unexpected as no toxicity was observed in preclinical models (16), and we have previously detected immunity to AR existing in patients with prostate cancer who otherwise had no evidence of autoimmunity (13). Most vaccine trials in prostate cancer to date have focused on tissue-restricted antigens, assuming that toxicity might be greater to antigens shared by normal tissues. Certainly that has not been the experience for other tumor types targeting antigens (e.g., CEA or HER-2/neu) with wider tissue expression profiles (23, 24). Hence, we expect that the increased expression of AR in prostate cancers, and notably after ADT, may favor this as an immunologically targetable antigen.

As described above, we found that immunization elicited T-cell responses to the AR LBD, but not antibody responses. This is consistent with preclinical findings in mice in which we also observed that DNA immunization favored the generation of CD4 and CD8 T cells rather than antibody responses (15). We have similarly found that a different DNA vaccine, encoding the prostate antigen prostatic acid phosphatase (PAP, ACP3), elicited Th1-type T-cell responses but not antibody responses in patients with prostate cancer (25). We assume that the immunity to AR elicited is Th1/Tc1-biased given that we observed IFNγ- and granzyme B-secreting responses. Further analyses are ongoing to identify whether antigen-specific Th2- or Th17-type responses may have been elicited in some individuals, and whether the responses observed were primarily CD4 or CD8 T cells. Of note, while all patients were immunized with tetanus toxoid, we did not detect T-cell responses in all individuals. We believe this is due to our definition of immune response, requiring detection at least 3-fold over baseline, which may be too stringent to detect responses in individuals with high preexisting immunity. Antibody responses to tetanus, however, were common, and identifiably augmented in the majority of patients.

A previous retrospective review of tumor vaccine trials found that traditional dose-escalation phase I trial designs were not useful in identifying doses for subsequent trials because, as opposed to standard cytotoxic therapeutic approaches, immune response may not be strictly dose-dependent, and few toxicities were identified at higher doses (26). For this trial, we elected to evaluate the treatment schedule, rather than dose, in particular because the vector backbone used for the pTVG-AR plasmid is identical to that previously used in other trials using a different DNA vaccine targeting PAP (pTVG-HP). In those previous trials, we had fixed the dose at 100-μg of plasmid DNA as one that demonstrated biological activity in eliciting T-cell immunity to the PAP-targeted antigen and was observed to be safe and well tolerated (20, 21, 25). The trial schedules evaluated in the current trial were based on one previously identified in previous human trials using pTVG-HP using several immunizations at 2-week intervals followed by intermittent boosters (20), or one with a more intermitted schedule evaluated in animal studies using pTVG-AR (15). Using magnitude and durability of immune response to AR as markers of biological activity, we identified the schedule of Arms 1 and 3 to be a preferred schedule of immunization. Specifically, we found that several repetitive immunizations appear necessary to elicit a consistent, detectable T-cell response. These findings are consistent with findings in a previous trial in which we evaluated the frequency of immunizations to elicit and maintain Th1-type immunity to the PAP-targeted antigen (20). Optimal immunization schedules remain unknown for human vaccines, and likely differ in the contexts of preventative vaccines for infectious diseases and for treating cancer in which the target antigen persists. Nonetheless, it appears that multiple repetitive immunizations are necessary. While it is believed that breaks in schedule may help establish T-cell memory, episodic booster immunizations may be necessary to maintain immune responses elicited.

Curiously, we did not identify a greater immune response when GM-CSF was used as a vaccine adjuvant. This was somewhat unexpected, as GM-CSF has been used as an adjuvant for many other vaccines. This has included cellular vaccines modified to secrete GM-CSF (27), and the only current FDA-approved cancer vaccine, sipuleucel-T, includes GM-CSF as part of the antigen used for activating antigen-presenting cells ex vivo (28). GM-CSF has also been used as a protein adjuvant, codelivered with the antigen. In particular, human trials using the hepatitis B vaccine have demonstrated improved immune responses when codelivered with GM-CSF (29, 30). Notwithstanding, a large trial evaluating GM-CSF as an adjuvant with a peptide vaccine demonstrated inferior immunity when used with GM-CSF (31). While GM-CSF has demonstrated utility as an adjuvant for DNA vaccines in animal models (32), it has not specifically been evaluated in randomized human trials using DNA vaccines. It is conceivable that bacterial plasmid DNA itself has an adjuvant effect, and little is added by the addition of GM-CSF protein. Certainly, preclinical studies in mice and rats with the pTVG-AR vaccine have demonstrated efficacy without the use of an additional adjuvant (15–17). Future clinical trials using the pTVG-AR vaccine will be done without GM-CSF adjuvant.

We found that vaccination was associated with immune responses to PSA, a nontargeted prostate-specific antigen. These findings are consistent with AR-targeted vaccination eliciting antigen spread, notably because immune responses to PSA were only detected in individuals who developed immunity to the AR LBD antigen. All patients were immunized with tetanus toxoid, and several patients developed response to tetanus but not the AR. The absence of response to PSA in these individuals suggests that immune responses to PSA detected were indeed a result of antigen spread. We have previously observed responses to PSA after treatment with pTVG-HP, and others have reported immune responses elicited to PSA as evidence of off-target antigen spread (20, 33). Future studies will further explore the character of T cells elicited to PSA, and the repertoire of tumor-infiltrating T cells following vaccination.

The major limitation of this study was the small sample size, notably given the inclusion of patients with different prior treatments (surgery, radiotherapy, or no prior therapy) and volume of disease. We expect that patients with recurrent prostate cancer after extirpative therapy, compared with patients with de novo metastatic disease, may have a prolonged time to progression. Hence, clinical outcomes must be interpreted cautiously. This may, in fact, explain some differences in progression with respect to the different treatment arms because more patients in Arms 2 and 4 had undergone prior prostatectomy. Notwithstanding, our studies suggest that successful immunization to the AR, as demonstrated by the detection of Th1 immunity to the AR-targeted antigen, was associated with delayed development of castration resistance. These are similar to our previous preclinical findings that immunization with this same vaccine led to prolonged survival of prostate tumor-bearing mice and rats, and prolonged time to castration resistance in mice treated with androgen deprivation (17). In addition, the time to castration resistance was similar for patients without evidence of immunity to the AR LBD to what has been observed in recent large clinical trials in this same population using standard androgen deprivation, and substantially longer in those patients with immunity (3, 5).

Taken together, these findings support the further evaluation of this vaccine in a phase II trial in patients with metastatic prostate cancer designed to rigorously evaluate whether treatment can prolong the time to castration resistance. When this trial began, docetaxel was the only agent demonstrated to prolong time to progression and overall survival when used concurrently with standard androgen deprivation for patients with mCSPC (2). Since this trial was conducted, several androgen-targeted therapies, including abiraterone, enzalutamide, and apalutamide, have also been approved for use in combination with standard androgen deprivation, based on similar improvement in time to progression and overall survival (3–5). Because overexpression of AR is likely a mechanism of resistance to all of these AR-targeted therapies, we expect that targeting the AR by vaccination should similarly prolong the time to castration resistance with any of these approaches. Hence, phase II trials using pTVG-AR will be conducted using standard androgen deprivation with other AR-targeting agents. Of note, a trial evaluating this vaccine in combination with PD-1 blockade is also underway in patients with castration-resistant metastatic prostate cancer (NCT04090528).

J. Eickhoff reports grants from Madison Vaccines, Inc. during the conduct of the study. A.C. Ferrari reports other from Rutgers Cancer Institute of New Jersey (Clinical trial contract, Madison Vaccines, Inc.) during the conduct of the study. M.T. Schweizer reports institutional funding from Madison Vaccines during the conduct of the study; institutional funding from Janssen, AstraZeneca, Pfizer, Hoffman-La Roche, and Zenith Pharmaceuticals, and personal fees from Janssen (consulting fee) outside the submitted work. B.M. Olson reports grants from Boehringer Ingleheim RCV GmbH & Co KG, Vaccinex Inc., and Bristol Meyers Squibb outside the submitted work; in addition, B.M. Olson has a patent (U.S. Patent No. 10,561,716 B2) on “Prostate cancer vaccine” issued, licensed, and with royalties paid from Madison Vaccines Incorporated and a pending patent (U.S. Patent No. US20170354725A1) on “Combinatorial androgen deprivation with an androgen receptor vaccine.” D.G. McNeel reports grants and personal fees from Madison Vaccines, Inc. (previous research support, ownership and consulting) during the conduct of the study; clinical trial support from Janssen and Pfizer, grants from Merck (clinical trial support), and non-financial support and other from BMS (clinical trial support) outside the submitted work; in addition, D.G. McNeel has a patent for a DNA vaccine targeting AR LBD issued and licensed to Madison Vaccines, Inc. No potential conflicts of interest were disclosed by the other authors.

C.E. Kyriakopoulos: Supervision, investigation, writing-review and editing. J. Eickhoff: Formal analysis, visualization, writing-review and editing, study biostatistician. A.C. Ferrari: Supervision, writing-review and editing, PI at clinical trial site. M.T. Schweizer: Supervision, writing-review and editing, PI at clinical trial site. E. Wargowski: Formal analysis, investigation, writing-review and editing, immunology data and analysis. B.M. Olson: Conceptualization, funding acquisition, writing-review and editing, design of protocol and immune analysis. D.G. McNeel: Conceptualization, resources, supervision, funding acquisition, writing-original draft, project administration, writing-review and editing.

This work was supported by the NIH R01 CA142608 (to B.M. Olson and D.G. McNeel), CA219154 (to E. Wargowski and D.G. McNeel), P30 CA014520 (to C.E. Kyriakopoulos, J.C. Eickhoff, and E. Wargowski), and by Madison Vaccines Inc (to C.E. Kyriakopoulos, A.C. Ferrari, M.T. Schweizer, and D.G. McNeel). We are grateful for the assistance of the research staff of the UWHC infusion center, University of Wisconsin pharmacy research center, clinical research staff, referring physicians, and the participation of the patients.

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