Tumor-specific neo-antigens that arise as a consequence of mutations are thought to be important for the therapeutic efficacy of cancer immunotherapies. Accumulating evidence suggests that neo-antigens may be commonly recognized by intratumoral CD8+ T cells, but it is unclear whether neo-antigen-specific CD4+ T cells also frequently reside within human tumors. In view of the accepted role of tumor-specific CD4+ T-cell responses in tumor control, we addressed whether neo-antigen-specific CD4+ T-cell reactivity is a common property in human melanoma.

Recognition of neoantigens that are formed as a consequence of DNA damage is likely to form a major driving force behind the clinical activity of cancer immunotherapies such as T-cell checkpoint blockade and adoptive T-cell therapy. Therefore, strategies to selectively enhance T-cell reactivity against genetically defined neoantigens are currently under development. In mouse models, T-cell pressure can sculpt the antigenicity of tumours, resulting in the emergence of tumours that lack defined mutant antigens. However, whether the T-cell-recognized neoantigen repertoire in human cancers is constant over time is unclear. Here we analyse the stability of neoantigen-specific T-cell responses and the antigens they recognize in two patients with stage IV melanoma treated by adoptive T-cell transfer. The T-cell-recognized neoantigens can be selectively lost from the tumour cell population, either by overall reduced expression of the genes or loss of the mutant alleles. Notably, loss of expression of T-cell-recognized neoantigens was accompanied by development of neoantigen-specific T-cell reactivity in tumour-infiltrating lymphocytes. These data demonstrate the dynamic interactions between cancer cells and T cells, which suggest that T cells mediate neoantigen immunoediting, and indicate that the therapeutic induction of broad neoantigen-specific T-cell responses should be used to avoid tumour resistance.

It is unknown how B cells that mature during a germinal center reaction 'decide' between plasma or memory cell fate. Here we describe a previously unknown subpopulation of B cells in the human germinal center that is characterized by tyrosine phosphorylated transcriptional activator STAT5. These cells had an activated centrocyte phenotype and had abundant expression of BCL6 but low expression of PRDM1, both encoding transcriptional repression proteins. Using RNA interference and ectopic expression of constitutively activated forms of STAT5, we demonstrate here a function for STAT5 in the self-renewal of B cells in vitro. STAT5b isoform seemed to directly upregulate Bcl-6, and ectopic expression of Bcl-6 in B cells resulted in self-renewal and inhibition of plasma cell differentiation. These data indicate that activation of STAT5 is involved in regulation of memory B cell differentiation.