CD34 and Epstein-Barr virus infection: The human T cells undergo positive and negative selection during maturation as indicated by the observation that the human cell-tropic EBV infection leads to effective anti-EBV T cell responses and circulating human T cells (or splenocytes) do not generate a mixed lymphocyte reaction (MLR) against human leukocytes from another hu-DKO mouse transplanted with human CD34+ HSC from the same donor but do generate an MLR against human leukocytes isolated from a hu-DKO mouse transplanted with CD34+ HSC from a different donor.