CD4 and acral lentiginous melanoma: In case studies, immunotherapy responses could be attributed to CD4 T cells, such as in a patient with metastatic cholangiocarcinoma who responded to adoptive transfer of neoantigen-specific CD4 TILs that directly recognized and killed tumor cells [177], or in a patient with a BRAF-mutant acral melanoma who sustained a complete clinical response after transfer of BRAFV600E-reactive CD4 TILs [309].