Background Our group developed a strategy for generating an ‘off-the-shelf’ multivalent proteasome-blocked autophagosome vaccine that contains proteins for many genes commonly overexpressed in adenocarcinoma and squamous cell cancers. This strategy exploits in vitro manipulation of the antigen presentation pathway to concentrate the dominant epitopes presented by MHC, including short-lived proteins (SLiPs), defective ribosomal products (DRiPs), and Dark Matter, the short-lived non-canonical peptides that are not expressed in the thymus and represent potential shared alternative cancer neoantigens.¹ In preclinical models this vaccine strategy provides significant protection as a single agent,² and significantly increased therapeutic efficacy when combined with anti-GITR and anti-PD-1.³ Based on these studies we hypothesize that addition of anti-GITR to the human vaccine, DPV-001, and anti-PD-1, will augment expansion and limit contraction of the anti-cancer immune response. A phase I clinical trial was initiated, and preliminary immunological monitoring data will be presented.

Methods Patients received DPV-001, with sequenced checkpoint inhibition (aPD-1 mAb; retifanlimab), with or without aGITR agonist mAb (INCAGN1876), in recurrent or metastatic HNSCC (NCT04470024). Tumor biopsies were taken pre-treatment, week 2 and 8. Blood samples were taken pre-treatment and at multiple timepoints and analyzed by flow cytometry and seromics. Tumor biopsies and blood were assayed by CITE-seq, scRNA-seq, BCR-seq, and TCR-seq. Multiplex immunofluorescence (mIF) was performed on biopsies.

Results In the first 4 patients evaluated, tumor-infiltrating T cells at week 8 increased from pre-treatment levels by an average of 4.3 fold (range 2.9 – 6.7, p=0.032). The density of CD39/CD103 double positive cells, previously shown to identify tumor-reactive T cells,⁴ also increased in all week 8 biopsies (mean 14.7 fold, range 5–40). All patients showed increased numbers of cells expressing IFN-γ and GZMB and increased numbers of T cells expressing LAG3+ in week 8 biopsies. Preliminary TCR evaluation of the tumor identified proliferation of clones previously undetected in PBL, including αβ T cells, iNKT and MAIT cells. Expansion of clones that predated treatment was also identified.

Conclusions An increase in intra-tumoral T cells expressing activation and effector molecules is encouraging and studies are underway to expand the number of patients analyzed. Increased expression of LAG3 by T cells that infiltrate and have expanded in the tumor, provide a rationale for including anti-LAG-3 in this treatment strategy. Future plans include evaluating whether immune responses target shared non-canonical alternative neoantigens, or Dark Matter, contained in DPV-001 and whether antibody responses identify targets of cellular immunity.

Acknowledgements Support: Incyte, UbiVac, Providence Medical Foundation, The Chiles Foundation, The Harder Family, Nancy Lematta, Robert W. Franz and Elsie Franz Finley, The Murdoch Memorial Trust

Trial Registration NCT04470024

References

1. Fox BA, Urba WJ, Jensen SM, Page DB, Curti BD, Sanborn RE, Leidner RS. Cancer’s Dark Matter: Lighting the Abyss Unveils Universe of New Therapies. Clinical Cancer Research 2023; 29:2173–2175. 10.1158/1078–0432.CCR-23–0422.

2. Twitty CG, Jensen SM, Hu H-M, Fox BA. Tumor-Derived Autophagosome Vaccine: Induction of Cross-Protective Immune Responses against Short-lived Proteins through a p62-Dependent Mechanism. Clinical Cancer Research 2011; 17:6467–6481. 10.1158/1078–0432.CCR-11–0812.

3. Patel JM, Cui Z, Wen Z-F, Dinh CT, Hu H-M. Peritumoral administration of DRibbles-pulsed antigen-presenting cells enhances the antitumor efficacy of anti-GITR and anti-PD-1 antibodies via an antigen presenting independent mechanism. J Immunother Cancer 2019; 7:311. 10.1186/s40425–019-0786–7.

4. Duhen T, Duhen R, Montler R, Moses J, Moudgil T, de Miranda NF, Goodall CP, Blair TC, Fox BA, McDermott JE, et al. Co-expression of CD39 and CD103 identifies tumor-reactive CD8 T cells in human solid tumors. Nat Commun 2018; 9:2724. 10.1038/s41467–018-05072–0.

Ethics Approval PSJH IRB# 2020000480