Natl. Inst. Radiol. Sci. Ann. Rept. (NRIS—10, 197 ) in the table, common clone cells in the two tissues ‘ did exist in cases B-17 and Th-3. In case B-17, one of the fishermen exposed to =- 4 = fallout radiation at Bikini in 1954, a clone with a roe e af marrow with a frequency of about 10%. In the ° a z harvotype of 47, XY, mart+ occurred in the bone Qo. e blood cultures four of the 690 cells (0.58%) showed a e z : * oO md ° e e e 5 500 1800 » 1500 8 7000 ne Mint Mur VALLES OF NEUTROPHILS Fig. LO. Correlation between chromosome aberrations (Cs cells)and minimum values of neutrophils. the karvotype of this clone. In case Th-3, a man injected with Thorotrast in 1945, 21 of the 519 cells (4%) in the bone marrow and 70 of the 3,398 cells (27%) in the blood cultures showed an identical karyolype of 46, XY, Gq-?, t(2p-Gpr) In case RT-1, a cervie cancer with hypoplastic anemia received radio-therapy, nearly 100% of the cells in the bone marrow were members of a single clone showing a karyotype of 46, XX, t(Bpt+;Cq—) and the demvatives, but none of the 273 cells snalyzed in the blood cultures showed this karyotype. Common Clone Cells with Structural Chromosome Aberrations in Periphera! Lymphocytes and in Bone Marrow of [rradiated Humans Takaaki Ishihara, Sei-ichi Kohno and Toshiyuki Kumatori The Ph! chromosome in’ chronic granulocytic leukerma is known to be present in granulocytic, erythrocytic and megakaryoeylic cells in bone marrow, but not in peripheral lymphocytes which are stimulated to divide in culture responding to PHA. The evidence has led to an idea that those lymphocytes imght be developed from a separate line while the former three cell series are derived from a common stem cell. In mice and rats. on the other hand, the presence of multipotent lympho-hematopoietic stem cells has been suggested. As a means of approaching the problem on the derivation of lymphocytes in their relation to bone marrow cells in humans, three radiation-exposed individuals who showed presence of distinct clones with structural chromosome abnormalities in bone marrow were studied in order to find out whether or not clone cells common to penpheral lymphocytes and bone marrow are present. The results of the chromosome analysis both in the bone marrow and in the cultured lymphocytes of the three cases are presented in Table 2. An seen 2el 1014830 The identification of cells with the same radiation-induced markers among the dividing cells in PHA-stimulated lymphocytes and in bone marrow in cases B-17 and Th-3 seems to be conclusive evidence for the presence of a lympho-hematopoietic stem cell in man yielding both lymphoid and bone marrow descendants. The present data from irradiated humans clearly demonstrated that PHA-responsive peripheral ly mphocytes are the progeny of the same stem cell for bone marrow cells, but they do not explain the reason for the absence in peripheral lymphocytes of cells with the Ph! chromosomein chronic granu- locytic leukemia or of the clone cells of case RT-I, which are observed as the majonty of the cells in bone marrow. This is a serious problem to be solved in future. (Unpublished)