A clinical trial of therapeutic vaccination in lymphoma with serial tumor sampling and single cell analysis.

In situ vaccination (ISV) triggers an immune response to tumor-associated antigens at one tumor site that can then tackle disease throughout the body. Here we report clinical and biological results of a phase I/II ISV trial in patients with low-grade lymphoma (NCT02927964) combining an intratumoral TLR9 agonist with local low-dose radiation, and ibrutinib (an inhibitor of B and T cell kinases). Adverse events were predominately low grade. The overall response rate was 50%, including one complete response. All patients experienced tumor reduction at distant sites. Single cell analyses of serial fine needle aspirates from injected and uninjected tumors revealed correlates of clinical response, such as lower CD47 and higher MHCII expression on tumor cells, enhanced T and NK cell effector function, and reduced immune suppression from TGFß and inhibitory T regulatory 1 cells. While changes at the local injected site were more pronounced, changes at distant uninjected sites more often associated with clinical responses. Functional immune response assays and tracking of T cell receptor sequences provided evidence of treatment-induced tumor-specific T cell responses. Induction of immune effectors and reversal of negative regulators were both important in producing clinically meaningful tumor responses. NCT02927964.