First-in-Human Phase I Trial of a Tumor-Targeted Cytokine (NHS-IL12) in Subjects with Metastatic Solid Tumors

Interleukin-12 (IL12), a proinflammatory cytokine produced by activated phagocytes and dendritic cells (DC), is critical to regulating the transition from innate to adaptive immunity. IL12 acts directly on natural killer (NK), NKT, and CD8⁺ T cells to stimulate proliferation and increase their cytotoxic functions (1). IL12 drives differentiation of helper T cells down the Th1 pathway, thereby promoting production of cytokines, notably IFNγ, that favor cell-mediated immunity (2). IL12 also acts directly on DCs to further stimulate IL12 production and enhance antigen presentation (3). Administration of exogenous IL12 thus could promote effective antitumor immune responses by amplifying these positive immunostimulatory effects.

However, recombinant (r) IL12 is not approved for any indication. A narrow therapeutic window with previously evaluated forms of systemic administration may have limited its ability to induce objective responses, delaying further clinical development (4, 5). To mitigate the side effects caused by systemic exposure, some early studies were done with intratumoral injections with viral vectors encoding IL12; however, this approach is logistically demanding (6). Furthermore, IL12 induces a counterregulation, making subjects temporarily less sensitive to the effects of IL12. This counterregulation is mediated by the induction and release of Th2 cytokines, such as IL10, which negates the IL12 response (7). If repeated doses of rIL12 are administered during this period of decreased sensitivity, increases in serum IFNγ are sharply reduced compared with levels induced by the initial dose of rIL12.

rIL12 has nonetheless shown promising clinical activity in phase I trials (8), showing an ability to induce antitumor immune responses at the maximum tolerated dose (MTD) over an extended period (9). Higher objective response rates with rIL12 have been reported in certain neoplastic diseases, including T-cell lymphoma (56%; ref. 10), non-Hodgkin lymphoma (21%; ref. 11), and AIDS-related Kaposi sarcoma (50%–71%; ref. 12).

NHS-IL12 may reduce toxicities associated with systemic administration of recombinant human IL12 by altering pharmacokinetics (PK) and selectively targeting IL12 to tumors. The NHS antibody component selectively targets human lung carcinomas as a radiolabeled monoclonal antibody (13). The NHS-IL12 immunocytokine is composed of two IL12 heterodimers, each fused to one of the H chains of the NHS76. This antibody targets IL12 to regions of tumor necrosis by binding to histones on free DNA fragments in these areas, thus increasing intratumoral exposure and reducing systemic exposure (14). This targeted strategy could reduce systemic toxicity and increase immune infiltration and activity within the tumor microenvironment (15), in turn priming otherwise nonimmunogenic tumors to checkpoint inhibition and increasing the spectrum of cancers that may respond to these agents.

Data from both in vitro assays using human peripheral blood mononuclear cells (PBMC) and in vivo primate studies showed that immune cells produce less IFNγ following treatment with NHS-IL12, suggesting less toxicity than rIL12 alone (13). NHS-IL12 up to 0.8 mg/m² was safely administered systematically to dogs and produced both immunologic and clinical activity (14), including complete regression of a 4.4-cm malignant melanoma. NHS-IL12 was also superior to rIL12 as an antitumor agent in 3 murine tumor models (13). Mechanistic studies all indicated that the antitumor effects of NHS-IL12 were primarily CD8⁺ T-cell–dependent and likely IL12 mediated.

This phase I study evaluated the safety, tolerability, PK, biological and clinical activity, effects on immune cell subsets, and T-cell receptor (TCR) clonality of NHS-IL12 in subjects with metastatic or locally advanced solid epithelial or mesenchymal tumors.

Eligible subjects had histologically or cytologically verified metastatic or locally advanced solid epithelial or mesenchymal tumors. All had completed, or progressed on, at least one prior therapy for metastatic disease, or were not candidates for therapy of proven efficacy for their disease. Subjects were ≥18 years old, had an Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 2, and had adequate organ function. Subjects had no history of autoimmune disease. The study protocol (NCT01417546) was approved by the NCI's Institutional Review Board, all subjects gave written informed consent, and the study was conducted in accordance with all institutional and federal guidelines.

Toxicities, graded using the NCI Common Terminology Criteria for Adverse Events v.4.0, were identified by medical history, physical examination, and laboratory studies. A dose-limiting toxicity (DLT) was defined as any grade ≥4 hematologic toxicity or grade 3 thrombocytopenia with associated bleeding and any grade ≥3 nonhematologic toxicity, with minor exceptions, that was definitely, probably, or possibly related to administration of NHS-IL12.

This phase I, open-label, single- and multiple-dose escalation study evaluated the MTD of NHS-IL12 monotherapy given subcutaneously (s.c.) as a single dose or every 4 weeks (see Table 1). Subjects were enrolled in cohorts of 3 to 6 using a standard 3 + 3 approach until MTD was reached. Dose level 8 enrolled 11 additional subjects in an expansion cohort evaluating biomarker analysis, immune infiltration of tumor, and response to treatment.

In the single-dose cohort, subjects received 1 dose of NHS-IL12 and were then followed for 28 days. In the multiple-dose escalation cohort, subjects received NHS-IL12 every 4 weeks at 2, 4, 8, 12, 16.8, and 21.8 μg/kg and then were observed for ≥6 weeks to evaluate DLTs.

Tumor responses were assessed by CT scan of the chest, abdomen, and pelvis after every 2 treatments or 8 weeks, or, for subjects with nonmeasurable but evaluable disease, after every 4 treatments or every 16 weeks based on clinical judgment and subject preference. Responses were assessed by modified immune-related RECIST criteria. For immune-related response criteria (irRC), only index and measurable new lesions were taken into account. Overall responses were derived from changes in index, nonindex, and new lesions.

PK parameters, including T_1/2, C_max, and AUC, were determined after single and multiple s.c. doses of NHS-IL12. Pharmacodynamic (PD) data were also collected and analyzed, including changes in serum levels of cytokines (IFN γ, IL10, IL6, IL8, IL4, and TNFα) using a multiplex cytokine/chemokine kit (Meso Scale Discovery) and the human IP-10 Instant ELISA kit (eBioscience) per the manufacturer's instructions. Biopsies were collected for analysis of TCR clonality, CD8 and CD4 memory/effector cells, regulatory T cells (Treg), NK cells, and DCs.

Flow cytometry was performed as previously described (16) using 4 panels of antibodies to identify 9 immune cell subsets, including CD4⁺ and CD8⁺ T lymphocytes, Tregs, NK cells, NKT cells, B lymphocytes, conventional and plasmacytoid DCs, and myeloid-derived suppressor cells, and 114 additional refined subsets relating to the maturation/function of standard subsets. All values were reported as a percentage of PBMCs to eliminate bias that could occur in smaller populations with fluctuations in parental leukocyte subpopulations (17). Only subsets with a frequency of ≥0.01% of PBMCs were considered. Statistical analyses were performed using GraphPad Prism 7 (GraphPad Software), using Wilcoxon paired samples test for comparisons between 2 time points. P values were adjusted for the large number of subsets evaluated using Holm method and adjusting within each major subset.

DNA was extracted from fresh frozen liver metastases and cryopreserved PBMCs before and after therapy with NHS-IL12 using the Qiagen DNeasy Blood and Tissue Kit (Qiagen). TCR Vβ CDR3 sequencing (TCRseq) was performed at the NCI genomic core facility (Frederick, MD) using the survey (tumor) or deep (PBMC) resolution Immunoseq platform (Adaptive Biotechnologies); analysis was performed using the ImmunoSeq ANALYZER 3.0 (Adaptive Biotechnologies). Repertoire size, a measure of TCR diversity, was determined by calculating the number of individual clonotypes represented in the top 25th percentile by ranked molecule count after sorting by abundance. Tumor-infiltrating lymphocyte (TIL) density was calculated from TCRseq data based on a human genome weight of 6.6 pg/cell: TIL density = (# productive templates)/(DNA input (pg)/6.6).

Summary statistics used to describe the study population included means, medians, ranges, and appropriate measures of variability for all demographic and baseline performance status characteristics. Results of safety evaluations were tabulated and displayed by dose level. Except for a few comparisons of biologic parameters, only exploratory statistical analyses were performed due to the limited number of subjects receiving each dose level. Descriptive statistics were examined for indications of dose-related toxicity.

Altogether, 59 subjects were treated with NHS-IL12. The single ascending-dose cohort had 22 subjects who received a single dose of NHS-IL12 on day 1 and completed the study after 28 days of safety observation (see Table 1). In the multiple ascending-dose and expansion cohorts, 37 subjects were treated every 4 weeks.

The median treatment duration in the multiple ascending-dose cohort was 70.0 days (range, 28–1,410+), with a median 2.5 doses administered (range, 1–47+). The 17 subjects treated at 16.8 μg/kg MTD (dose level 8) received a median 2 doses (range, 1–8).

PK data from the single- (Supplementary Table S1A) and multiple-dose (Supplementary Table S1B) cohorts show a dose-dependent increase in T_1/2, C_max, and AUC for NHS-IL12. PD data (Fig. 1A) demonstrate a time-dependent rise in IFNγ after administration and an associated rise of IL10 (Supplementary Fig. S1). These correspond to a similar rise in IL12 seen in the PK data, peaking around 36 hours and then falling to near baseline around day 8. In most multiple-dose subjects, despite a similar rise in serum IL12, IFNγ and IL10 rose to a lesser degree after the second dose. Figure 1A shows PD results for subjects dosed at the MTD of 16.8 μg/kg every 4 weeks (dose level 8). Supplementary Figs. S2, S3, and S4 show PD results for dose levels 6, 7, and 9, respectively.

Similar trends were seen for serum levels of IFNγ-inducible protein (IP-10, CXCL10; Fig. 1B), a chemokine secreted by macrophages after stimulation by IFNγ that acts as a chemoattractant for activated T cells and inhibits neovascularization (18). We found highly increased levels after cycle 1 and lesser increases after cycle 2. The highest levels were found in subjects treated at the highest doses of NHS-IL12 (Fig. 1B).

The primary objective of this trial was to determine MTD as defined by the number of DLTs. None of the subjects treated with single or multiple doses up to 12.0 μg/kg experienced a DLT. At 16.8 μg/kg, 1/6 subjects had a DLT [grade 3 increase in alanine transaminase (ALT)]. At 21.8 μg/kg, 2/6 subjects had a DLT [grade 3 increase in aspartate transaminase (AST) and ALT; grade 3 increase in lipase without clinical signs of pancreatitis]. MTD was 16.8 μg/kg.

The most frequently observed treatment-related adverse event (TRAE) was decreased lymphocyte count (27/59 subjects; 45.8%). Other TRAEs included decreased white blood cells (WBC; 24/59; 40.7%), fever and elevated AST (21 each; 35.6%), elevated ALT (20; 3.9%), and anemia and flu-like symptoms (18 each; 30.5%; Table 2; Supplementary Fig. S5). Among the cohort receiving 16.8 μg/kg, the most frequently reported TRAEs were elevated AST (75%), decreased WBCs and elevated ALT (68.8% each), and decreased lymphocyte count and fever (62.5% each).

At least one grade ≥3 TRAE was seen in 12/59 subjects (20.3%). These included decreased lymphocyte count (5; 8.5%), decreased neutrophil count (4; 6.8%), elevated ALT (3; 5.1%), decreased WBCs (2; 3.4%), and hypokalemia, hyperhidrosis, elevated alkaline phosphatase, AST, and lipase (1 each; 1.7%). All grade ≥3 TRAEs were transient; only hyperhidrosis was symptomatic. One grade 4 TRAE was observed (asymptomatic decreased lymphocyte count); no grade 5 TRAE was observed. Toxicity was slightly worse at 16.8 μg/kg, with 5/17 subjects (29.4%) experiencing at least one grade ≥3 TRAE. Overall, 48 subjects (81.4%) experienced TRAEs (Table 2); only 2 (3.4%) were serious.

No objective tumor responses were observed according to modified RECIST criteria. Of 30 subjects with measurable disease, 15 had stable disease and 15 had progressive disease as best overall response. Five subjects (prostate ×2, colorectal, breast, chordoma) stayed on study for ≥182 days. One subject with prostate cancer and one with chordoma had prolonged stable disease (30+ months and 13 months, respectively).

Multicolor flow cytometry was used to evaluate 123 discrete immune cell subsets, including 9 standard subsets and 114 refined subsets, as previously described (16). All 123 immune cell subsets were evaluated on days 1 and 8, 1 week after the first dose, in 10 subjects receiving 16.8 μg/kg of NHS-IL12 (dose level 8). Frequencies of activated (Tim3⁺) NK cells, mature NK cells, and PD-1⁺ NKT cells increased (Fig. 2). Frequencies of terminally differentiated PD-L1⁺ CD4 T cells (CD4-EMRA) and plasmacytoid DCs decreased, while frequencies of the 9 standard immune cell subsets remained unchanged 1 week after therapy. PBMCs were also available from 13/17 subjects at dose level 8 for multicolor flow cytometry at baseline and day 57 after 2 cycles of NHS-IL12. Of the 9 standard subsets, only the frequency of NKT cells increased significantly from days 1 to 57 (Supplementary Table S2). No other subsets changed significantly.

Three pre- and posttreatment paired biopsies were evaluated using the MultiOmyx mIF-IHC TIL Panel (NeoGenomics) to assess potential NHS-IL12–induced changes in immune cell infiltration and PD-L1 expression. A trend toward increased PD-L1 expression was detected in 2/3 pairs. No large changes in various immune cell readouts were observed; however, sample size was limited.

To investigate whether NHS-IL12 induces remodeling of the T-cell repertoire, we performed TCRseq on available tumor biopsies and corresponding PBMCs pre- and post–NHS-IL12 from 4 subjects in the dose level 8 expansion cohort (Fig. 3A). Representative TCRβ clonotype frequency plots of the biopsy (Fig. 3B) and PBMCs (Fig. 3C) of a subject with a high systemic IFNγ response (PT58) are depicted pre- and post–NHS-IL12 therapy. TCR diversity increased 6- to 14-fold in biopsies of subjects with a high (PT58) or intermediate (PT57) IFNγ response, but was unchanged or decreased in biopsies of subjects with a low (PT51, PT59) IFNγ response (Fig. 3D).

We next investigated whether any unique clones expanded in the tumor and periphery after NHS-IL12 therapy. Up to 6 of the top 10 clones that increased the most in a subject's biopsy also increased in PBMCs (Table 3A); moreover, as many as 5 of the top 10 clones that increased the most in a subject's PBMCs also increased in the biopsy, but often to a lesser extent (Table 3B). TIL density (see Materials and Methods) also increased 1.3- to 8.6-fold in subjects with a high or intermediate IFNγ response, but decreased in subjects with a low IFNγ response (Fig. 3E).

PD data from this trial (Fig. 1A) demonstrated a time-dependent rise in IFNγ after treatment and an associated rise in IL10. Despite a similar rise in serum IL12, most multiple-dose subjects had a diminished rise in IFNγ and IL10 on the second dose. This observation is consistent with the finding that the second and subsequent doses of NHS-IL12 were generally better tolerated and had decreased toxicity compared with the first dose (Supplementary Table S3). These data also support the hypothesis that the frequency of NHS-IL12 may feasibly be increased to every 2 weeks with minimal risk for dose stacking and added toxicities. Based on these data, a 2-week dosing schedule is currently being evaluated. Although we have not seen responses with this agent at the doses and frequencies tested so far, more frequent dosing may lead to greater efficacy.

This therapy was evaluated in subjects with a wide array of locally advanced or metastatic cancers, many of which were refractory to multiple standard therapies. In addition, while NHS-IL12′s antitumor activity may be modest as a monotherapy, a great deal of preclinical data suggest that its combination with other treatment modalities, including radiation, chemotherapy, or other immunotherapies, may improve antitumor responses (13, 15, 19). For example, the combination of NHS-IL12 with localized fractionated radiotherapy, sunitinib, or gemcitabine showed additive tumor growth inhibition relative to these agents as monotherapies (13, 20). The combination of NHS-IL12 and avelumab has also been shown to enhance antitumor efficacy more than either therapy alone in multiple murine tumor models (21). Antitumor efficacy correlated with higher frequency of tumor antigen-specific splenic CD8⁺ T cells and enhanced T-cell activation over a wide range of NHS-IL12 concentrations. Based on these data, NHS-IL12 plus avelumab is now being evaluated (NCT02994953), and a number of clinical trials are planned to evaluate NHS-IL12 in combination with other therapies. Notably, the potential for combination of tumor-directed IL12 therapy plus checkpoint inhibitor therapy over checkpoint inhibitor therapy alone was recently demonstrated in KEYNOTE 695, a phase II trial evaluating intratumoral plasmid IL12 injection with electroporation in combination with pembrolizumab in patients with advanced melanoma. In this study, 11/22 patients (50%) who were deemed unlikely to respond to checkpoint inhibition, based upon baseline biomarker data, had an objective response, and 3/9 patients (33%) who had progressed on prior checkpoint inhibitor therapy developed objective responses. Because NHS-IL12 is an immunocytokine, one would expect to see changes in the peripheral immunome soon after treatment. The earliest that PBMCs were available for evaluation was 1 week after NHS-IL12 infusion, at which time there were increased levels of activated (Tim3⁺) and mature (CD16⁺ CD56^dim) NK cells, as well as PD-1⁺ NKT cells. These changes are expected, because it is well known that IL12 increases both proliferation and lytic capacity of NK cells (1). Levels of terminally differentiated CD4⁺ T cells and plasmacytoid DCs decreased. Similar changes were also observed 1 week after the second infusion (data not shown). In contrast, only NKT cells were still increased 2 months after treatment. Interestingly, NKT cells have a dual role in tumor progression and treatment, and when they are stimulated by self-antigens in the presence of IL12, they are among the first lymphocytes to become activated to promote antitumor responses by producing IFNγ and by stimulating IL12 production from myeloid DCs (22).

Sequencing of TCR CDR3 regions is a valuable technique for evaluating T-cell clonal representation in both tumors and peripheral blood. We performed TCRseq on tumor biopsies and matching PBMCs, where available, from 4 subjects with varying systemic IFNγ responses in the dose level 8 expansion cohort. Although only a very small number of subjects were assayed, the results demonstrate that subjects with a high/medium IFNγ response to NHS-IL12 had an increase in TIL density and TCR diversity within the tumor. This broadening of TCR diversity within the tumor suggests that NHS-IL12 may facilitate trafficking of T cells into the tumor, is consistent with other immunotherapy studies, and does not conflict with a concurrent focusing of an underlying antitumor immune response (23, 24). Comparison of TCRseq data from the biopsy and peripheral blood showed that some clones increased in both.

NHS-IL12 proved to be generally well tolerated, and preclinical data suggest its potential to improve antitumor responses when given with other standard treatments and immunotherapies. The next step will be to evaluate NHS-IL12 in combination therapy. Because NHS-IL12 can increase immune infiltration within the tumor microenvironment, it may also prime otherwise nonimmunogenic tumors to checkpoint inhibition and increase the spectrum of cancers responding to immunotherapy. Given this potential, multiple clinical studies are evaluating the combination of NHS-IL12 and checkpoint inhibition.

No potential conflicts of interest were disclosed.

Conception and design: C.R. Heery, M. Bilusic, J. Schlom, J.L. Gulley

Development of methodology: C.R. Heery, J.L. Gulley

Acquisition of data (provided animals, acquired and managed patients, provided facilities, etc.): J. Strauss, C.R. Heery, J.W. Kim, C. Jochems, R.N. Donahue, A.S. Montgomery, S. McMahon, E. Lamping, R.A. Madan, M. Bilusic, M.R. Silver, J. Schlom, J.L. Gulley

Analysis and interpretation of data (e.g., statistical analysis, biostatistics, computational analysis): J. Strauss, C.R. Heery, C. Jochems, R.N. Donahue, A.S. Montgomery, J.L. Marté, M.R. Silver, J. Schlom, J.L. Gulley

Writing, review, and/or revision of the manuscript: J. Strauss, C.R. Heery, J.W. Kim, R.N. Donahue, A.S. Montgomery, R.A. Madan, J. Schlom, J.L. Gulley

Administrative, technical, or material support (i.e., reporting or organizing data, constructing databases): J. Strauss, A.S. Montgomery, J.L. Gulley

Study supervision: E. Lamping, J.L. Gulley

Other (bioanalyses of clinical samples): E. Bertotti

This research was sponsored and supported by the Intramural Research Program of the Center for Cancer Research, NCI, NIH. EMD Serono supplied NHS-IL12 under a Cooperative Research and Development Agreement (CRADA) with the NCI.

The authors are indebted to the subjects who donated their tissue, blood, and time and to the clinical teams who facilitated subject informed consent, as well as sample and data acquisition. The authors thank Debra Weingarten for her assistance in the preparation of this article.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.