HLA-C and lymphopenia: Reconstitution of the T lymphocyte compartment of a lymphopenic host by HSC transplant or transfer of T cells results in LIP as the cells expand to fill the available niche defined by available peptide–MHC (pMHC) and cytokine “resources.” The relative abundance of resources in a host with respect to the numbers of competitors for those resources can be considered as a way to define the “severity” of lymphopenia in that host or its “LIP-potential” (40).