CTLA4 and cryohydrocytosis: Cytotoxic T lymphocyte-associated antigen (CTLA4), programmed cell death 1 (PD-1), Tim3 (T cell immunoglobulin and mucin-domain containing protein 3) are immune checkpoint receptors that deliver inhibitory signals to T cells and are highly expressed during CHC on exhausted and dysfunctional T cells [43,44,45].