Document resource
Background CD4 + T cells provide crucial supports to CD8+ T cell responses in the context of cancer vaccination. We and others have shown tumor antigen cognate-CD4+ T cells support cognate CD8+ T cells presence within recurrent tumors and enhance tumor control better than non-cognate CD4+ T cells in murine models.1 2 We recently showed that patients vaccinated with twelve MHC-I-shared melanoma peptides (12MP) plus six class-II-restricted melanoma helper peptides (6MHP; cognate help) had improved long-term clinical outcomes compared to those who received 12MP plus a class-II-restricted tetanus helper (non-cognate) peptide (Mel44; NCT00118274),3 despite weaker primary CD8+ & CD4+ T cell responses determined by IFNg ELISpot.4 IFNg, a major cytokine produced by Th1 cells, can drive CD8+ effector differentiation resulting in weaker memory development. We therefore hypothesize that 6MHP-specific CD4+ T cells are less Th1 differentiated and support memory CD8+ T cells development and/or enhance their recall capacity.Methods PBMCs isolated at the peak immune response and memory timepoints (week 104) from Mel44 patients vaccinated with12MP+6MHP or 12MP+tetanus were stained ex vivo with 12MP-specific MHC-I dextramers and evaluated by flow cytometry to determine the numbers and proportions of peak effector & memory CD8+ T cells.Results In the two patients evaluated so far, the frequency of effector CD8 + T cells was higher during primary response in the presence of non-cognate help, but the contraction of primary effectors to memory was dramatically more in patients with non-cognate help compared to those with cognate help (78% reduction vs. 27%, figure 1). Thus, cognate help generated in 6MHP vaccines resulted in durable circulatory antigen-specific CD8+ T cells after contraction compared to non-cognate help.Conclusions We have determined the proportion of memory CD8 + T cells in a pilot experiment and found that 6MHP vaccine preserved memory CD8+ T cells, providing initial support of the hypothesis. These findings suggest that tumor-cognate help may better preserve circulatory memory CD8+ T cells than non-cognate help. This may contribute to durable clinical outcome despite lower peak primary responses. Future work will determine the recall capacity of memory CD8+ T cells between the two vaccine regimens, using cytokine staining and proliferation assays. We will also evaluate the preservation of memory in a larger number of Mel44 patients, as well as assess the phenotypes of tumor cognate vs. non-cognate CD4+ T cells to test whether 6MHP-specific CD4+ T cells are indeed less Th1 differentiated.Trial Registration The human samples were obtained from a completed clinical trial (Mel44) registered with ClinicalTrials.gov. Trial registry number: NCT00118274References Hwang ML, Lukens JR, Bullock TN. Cognate memory CD4+ T cells generated with dendritic cell priming influence the expansion, trafficking, and differentiation of secondary CD8+ T cells and enhance tumor control. J Immunol. 2007 Nov 1;179(9):5829–38. doi: 10.4049/jimmunol.179.9.5829. PMID: 17947656.de Graaf JF, Pesic T, Spitzer FS, Oosterhuis K, Camps MGM, Zoutendijk I, Teunisse B, Zhu W, Arakelian T, Zondag GC, Arens R, van Bergen J, Ossendorp F. Neoantigen-specific T cell help outperforms non-specific help in multi-antigen DNA vaccination against cancer. Mol Ther Oncol. 2024 Jun 15;32(3):200835. doi: 10.1016/j.omton.2024.200835. PMID: 39040850; PMCID: PMC11261851.Ninmer EK, Zhu H, Chianese-Bullock KA, von Mehren M, Haas NB, Ross MI, Dengel LT, Slingluff CL Jr. Multipeptide vaccines for melanoma in the adjuvant setting: long-term survival outcomes and post-hoc analysis of a randomized phase II trial. Nat Commun. 2024 Mar 22;15(1):2570. doi: 10.1038/s41467-024-46877-6. PMID: 38519525; PMCID: PMC10959948.Slingluff CL Jr, Petroni GR, Chianese-Bullock KA, Smolkin ME, Ross MI, Haas NB, von Mehren M, Grosh WW. Randomized multicenter trial of the effects of melanoma-associated helper peptides and cyclophosphamide on the immunogenicity of a multipeptide melanoma vaccine. J Clin Oncol. 2011 Jul 20;29(21):2924-32. doi: 10.1200/JCO.2010.33.8053. Epub 2011 Jun 20. PMID: 21690475; PMCID: PMC3138719.Ethics Approval The human samples in this study were obtained from a completed clinical trial (Mel44). This trial was approved by the institutional review boards (IRB) at the 3 participating institutions (University of Virginia, MD Anderson Cancer Center at the University of Texas – Houston, and Fox Chase Cancer Center), with the University of Virginia at the lead institution; approval number: IRB-HSR #11491.Abstract 838 Figure 1Quantification of antigen-specific CD8+ T cells. PBMCs from two timepoints were stained with 12MP-dextramer and analyzed by flow cytometry (n=2 per group). Left represents the total counts of antigen-specific CD8+ T cells while the right represents the proportion out of total CD8+ T cells