Introduction: A breakthrough of immunotherapy for cancer treatment has emerged, with promising results in several tumors. We have developed the allogeneic vaccine CSF-470, composed of lethally-irradiated human Cutaneous Melanoma (CM) cell lines plus BCG and GM-CSF, currently tested in a Phase II-III study in adjuvancy (NCT01729663). The aim of this work was to analyze the TCRâ repertoire in multiples samples obtained through CSF-470 vaccination from a CM patient who developed a cutaneous metastasis (Mts) at the end of the 2-year immunization protocol.

Methods: DNA from PBMC at 0, 12 and 24 months (PRE-PBMC, POST-1, POST-3) from protocol start, and from Mts-TIL (Tumor Infiltrating Lymphocytes) was obtained. TCRâ sequence and further analysis was performed with the IMMUNOSEQ platform. Patterns were defined for clone tracking: 1, present at PRE, increases during immunization; 2, absent at PRE, increases during immunization; 3, present at PRE, absent following immunization; 4, present at PRE, decreases during immunization; 5, detected only at 24 months (POST-3); 6, absent at PBMC, present in Mts-TIL.

Results: PBMC TCRâ repertoire analysis revealed an increase in clonality (2.3X) and total frequency of TOP100 clones through CSF-470 immunization. PBMC clones tracking analysis (with frequency ≥0.01%) revealed prevalence of Pattern-1 clones (54%) and Pattern-5 clones (30%). Regarding Mts-TIL, clones were distributed in Pattern-1 (23%), Pattern-3 (5%), Pattern-5 (16%), and Pattern-6 (53%). However, when analyzing TOP100 Mts-TIL clones, 60% of them corresponded to Pattern-1, 19% to Pattern-5 and only 12% to Pattern-6. Databases search revealed the presence in PBMC of shared TCRâ sequences previously reported in association to M.bovis infection. Also, some clones found in Mts-TILs matched to previously identified in other CM metastases.

Conclusions: This is the first report of the TCRâ repertoire from a CM patient immunized with CSF-470 vaccine. The main observations regarding TCRâ repertoire analysis were: 1- Vaccination induced expansion of selected pre-immunization TCR clones, which might recognize dominant Ags either from patient′s tumor or vaccine. 2- TCR clones arising after immunization might recognize dominant Ags from vaccine or derived by epitope spreading from the patient′s tumor. 3- More than 50% of total clones were exclusively present in Mts-TIL, suggesting local activation. However, most frequent Mts-TIL clones included those that were expanded exclusively by CSF-470 vaccination. 4- TCRâ repertoire comparison also allowed detection of some clones already reported in TIL from CM Mts and in memory repertoire against M.Bovis, possibly accounting BCG adjuvancy.

Finally, changes observed in the TCRâ repertoire from this patient, driven by the CSF-470 vaccine, suggest an anti-tumor immune response taking place both in the periphery and the local compartment.

Citation Format: Mariana Aris, María Marcela Barrio, José Mordoh. First evidence of changes in the TCRâ repertoire from a cutaneous melanoma patient immunized with the CSF-470 vaccine. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4897.