Immunohistology of the human spleen after bone marrow transplantation for leukemia with special reference to the early post-transplantation period.

Immunohistochemical investigations were undertaken on paraffin-embedded tissue from the spleens of seven patients who had died after bone marrow transplantation (BMT) for leukemia. Parallel investigations were undertaken on three surgically resected traumatically ruptured (but otherwise normal) spleens and three spleens removed at autopsy from accident victims. 1) Up to ten weeks after BMT, the splenic lymphoid tissue was extremely atrophic. Lymphoid follicles (LFs) and periarteriolar lymphatic sheaths (PALS) were completely absent. A considerable increase in lymphoid cells in the red pulp and formation of small LFs and PALS occurred only in the longest surviving patient, who had died 50 weeks after BMT. 2) B cells (L26+, 4KB5+, Ki-B3+) were almost completely absent in the early post-transplantation period and thus T cells (UCHL1+) represented the major constituent of the hypoplastic splenic lymphoid tissue. Considerable numbers of T cells were already found two weeks after BMT. T-immune-accessory reticulum cells (S-100 protein+) were found in the PALS of the controls, but were absent in three of the BMT recipients. The findings clearly reflect the marked immunodeficiency in the early post-transplantation period, during which many patients (4/7 in this study) die of opportunistic infections, and are in line with the fact that the earliest signs of reconstitution of the immune system have been found to occur at three months post-transplantation. Since six of our BMT recipients had suffered from graft-versus-host disease our findings probably do not fully correspond to those when the immune system undergoes undisturbed reconstitution.