Spontaneous antitumor T cell responses in cancer patients

Mutated proteins arising from somatic mutations in tumors are promising targets for cancer immunotherapy. They represent true tumor-specific antigens (TSAs) as they are exclusively expressed in tumors, reduce the risk of autoimmunity and are more likely to overcome tolerance compared to wild-type (wt) sequences. Hence, we designed a panel of long peptides (LPs, 28–35 aa) comprising driver gene mutations in TP35 and KRAS frequently found in gastrointestinal tumors to test their combined immunotherapeutic potential. We found increased numbers of T cells responsive against respective mutated and wt peptides in colorectal cancer patients that carry the tested mutations in their tumors than patients with other mutations. Further, active immunization of HLA(-A2/DR1)-humanized mice with mixes of the same mutated LPs yielded simultaneous, polyvalent CD8+/CD4+ T cell responses against the majority of peptides. Peptide-specific T cells possessed a multifunctional cytokine profile with CD4+ T cells showing a TH1-like phenotype. Two mutated peptides (Kras[G12V], p53[R248W]) induced significantly higher T cell responses than corresponding wt sequences and comprised HLA-A2/DR1-restricted mutated epitopes. However, vaccination with the same highly immunogenic LPs strongly increased systemic regulatory T cells (Treg) numbers in a syngeneic sarcoma model over-expressing these mutated protein variants and resulted in accelerated tumor outgrowth. In contrast, tumor outgrowth was delayed when vaccination was directed against tumor-intrinsic Kras/Tp53 mutations of lower immunogenicity. Conclusively, we show that LP vaccination targeting multiple mutated TSAs elicits polyvalent, multifunctional, and mutation-specific effector T cells capable of targeting tumors. However, the success of this therapeutic approach can be hampered by vaccination-induced, TSA-specific Tregs.

T‑cell costimulation is necessary to induce a response of naïve T cells. Whether T‑cell costimulation can also cause reactivation of unreactive, possibly anergized memory T cells (MTCs) from late‑stage cancer patients is unknown. To investigate this question, we developed a bispecific anti‑CD28 fusion protein (bsHN‑CD28) which can easily be attached to the vaccine ATV‑NDV. This virus‑modified autologous tumor cell vaccine has already shown effectivity in colon cancer patients following resection of liver metastases. In this phase Ⅰ clinical study, 14 colorectal carcinoma (CRC) patients with late‑stage disease which could not be operated anymore with curative intent were treated with the vaccine ATV‑NDV to which bsHN‑CD28 was attached. No severe adverse events were recorded. All patients showed an immunological response of tumor‑reactive T cells, at least once during the course of five vaccinations. Also, we demonstrate a dose‑response relationship with the costimulatory molecule added to the vaccine. A partial response of metastases was documented in four patients. The study suggests that the three‑component vaccine is safe and can reactivate possibly anergized T cells from a chronic disease like advanced‑stage cancer.