Vaccination generates functional progenitor tumor-specific CD8 T cells and long-term tumor control.

Background: Immune checkpoint blockade (ICB) therapies are an important treatment for patients with advanced cancers; however only a subset of patients with certain types of cancer achieves durable remissions. Cancer vaccines are an attractive strategy to boost patient immune responses, but less is known about whether and how immunization can induce long-term tumor immune reprogramming and arrest cancer progression. We developed a clinically-relevant genetic cancer mouse model in which hepatocytes sporadically undergo oncogenic transformation. We compared how tumor-specific CD8 T cells (TST) differentiate in mice with early sporadic lesions as compared to late lesions and tested how immunotherapeutic strategies, including vaccination and ICB, reprogram TST and impact liver cancer progression.

Methods: Mice with a germline floxed allele of the SV40 large T antigen (TAG) undergo spontaneous recombination and activation of the TAG oncogene, leading to rare early pre-cancerous lesions that inevitably progress to established liver cancer. We assessed the immunophenotype and function of TAG-specific CD8 T cells in mice with early and late liver lesions. We vaccinated mice, either alone or in combination with ICB, to test whether these immunotherapeutic interventions could stop liver cancer progression.

Results: In mice with early lesions, a subset of TST were PD1 TCF1 TOX and could produce IFNγ, while TST present in mice with late liver cancers were PD1 TCF1 TOX and unable to make effector cytokines. Strikingly, vaccination with attenuated TAG epitope-expressing (LM ) blocked liver cancer development and led to a population of TST that were TCF1 TOX TST and polyfunctional cytokine producers. In contrast, ICB administration did not slow cancer progression or improve LM vaccine efficacy.

Conclusion: Vaccination, but not ICB, generated a population of progenitor TST and halted cancer progression in a clinically relevant model of sporadic liver cancer. In patients with early cancers or at high-risk of cancer recurrence, immunization may be the most effective strategy.

What Is Already Known On This Topic: Immunotherapy, including immune checkpoint blockade and cancer vaccines, fails to induce long-term remissions in most patients with cancer.

What This Study Adds: Hosts with early lesions but not hosts with advanced cancer retain a progenitor TCF1+ TST population. This population can be reprogrammed and therapeutically exploited by vaccination, but not ICB, to block tumor progression.

How This Study Might Affect Research Practice Or Policy: For people at high-risk of cancer progression, vaccination administered when a responsive progenitor TST population is present may be the optimal immunotherapy to induce long-lasting progression-free survival.