MSH2 and thymus lymphoma: Though hematopoiesis in young MSH2-deficient mice appears normal, the high incidence of thymic lymphomas [18,19] in MSH2-deficient mice lead us to hypothesize that MSH2-deficient HSCs are PLSCs, and the transformation of MSH2-deficient PLSC into LSC or LIC requires the thymus microenvironment.