Marrow graft rejection and inhibition of growth in culture by serum in aplastic anaemia

Integration of humoral and cellular HLA-specific immune responses in cord blood allograft rejection

In allo-stem cell transplantation (SCT), it is unclear whether donor-specific anti-HLA Abs (DSAs) can actually mediate graft rejection or if they are simply surrogate markers for the cellular immunity that causes graft rejection. Here, we first analyzed a case of cord blood allograft rejection in which DSA and cytotoxic T lymphocyte (CTL) specific for donor HLA-B*54:01 were detected at the time of graft rejection. Both the DSA and CTL inhibited colony formation by unrelated bone marrow mononuclear cells sharing HLA-B*54:01, suggesting that the humoral and cellular immune responses were involved in the graft rejection. Interestingly, the DSA and CTL were also detected in cryopreserved pre-transplant patient blood, raising a hypothesis that the presence of anti-HLA Abs could be an indicator for corresponding HLA-specific T cells. We then evaluated the existence of HLA-specific CD8(+) T cells in other patient blood specimens having anti-HLA class I Abs. Interferon-γ enzyme-linked immunospot assays clearly confirmed the existence of corresponding HLA-specific T-cell precursors in three of seven patients with anti-HLA Abs. In conclusion, our data demonstrate that integrated humoral and cellular immunity recognizing the same alloantigen of the donor can mediate graft rejection in DSA-positive patients undergoing HLA-mismatched allo-SCT. Further studies generalizing our observation are warranted.

Panel reactive antibody in thalassemic serum inhibits proliferation and differentiation of cord blood CD34+ cells in vitro

Thalassemic children are at a high risk of graft rejection in cord blood transplantation. To investigate this possible mechanism, the authors evaluated the effect of panel reactive antibody on the growth of CD34(+) cells in vitro. On semisolid medium, CD34(+) cells derived from cord blood were incubated with thalassemic serum, and colony-forming units were counted after 10 days of culture. After incubation with serum-specific panel reactive antibody, profound decreases were found in the numbers of CFU-GM, CFU-GEMM and BFU-E compared with controls. The results indicated that serum-specific panel reactive antibody might have an apparent inhibition effect on proliferation and differentiation of cord blood CD34(+) cells.

Allogeneic bone marrow transplantation for severe aplastic anaemia--the London experience

Using the Seattle protocol with minor modifications, 23 patients with severe aplastic anaemia received allogeneic bone marrow transplants from HLA/mixed leucocyte culture matched sibs in three London centres between 1973 and 1977. Ten patients (43.5%) are alive 6 months to 5 years after transplantation, and are well with full haemopoietic reconstitution, two with autologous bone marrow recovery following the graft procedure. A failure of the marrow graft to take, or take followed by rejection occurred in 12 patients (52%). Failure of marrow recovery was associated with a high early mortality from bacterial or fungal infection. The only survivors amongst those who rejected the first graft were four patients in whom a subsequent graft from the same donor was successful, and two in whom autologous recovery occurred. Graft versus host disease (GVHD) occurred in seven patients, and was fatal in one case. The most frequent complication after successful engraftment was varicella-zoster infection which occurred in five patients and was fatal in one patient. The overall results compare favourably with those from other transplant centres, but the high rate of graft rejection and low incidence of GVHD differ from other series. The results should encourage further referral of patients with severe AA for bone marrow transplantation.

Complement-dependent hematopoietic inhibitors in the sera of patients with aplastic anemia and paroxysmal nocturnal hemoglobinuria

The sera of 14 out of 48 patients with aplastic anemia and four out of nine patients with paroxysmal nocturnal hemoglobinuria (PNH) contained complement-dependent hematopoietic inhibitory activity against allogeneic marrow progenitor cells. Some sera with hematopoietic inhibitory activity, however, demonstrated no effect on autologous marrow progenitor cells. Hematopoietic inhibitory activity was absorbed by pooled, packed platelets. Serum hematopoietic inhibitory activity was present in both IgM and IgG fractions. These data suggested that serum hematopoietic inhibitors are alloantibodies and might be associated with graft rejection in the transplanted marrow of patients with aplastic anemia and PNH.

Haemopoietic stimulators and inhibitors in aplastic anaemia serum

Normal serum and serum from four patients with severe aplastic anaemia was fractionated by Sephadex G-150 gel filtration. Fractions were tested for direct haemopoietic activity on colony forming cells in methylcellulose cultures, and for their indirect influence on haemopoiesis via CSA- and BPA-producing cells. All aplastic anaemia sera contained abnormal inhibitors and stimulators. An inhibitor acting on both haemopoietic and factor producing cells, eluting with the IgM fraction was found in all, variable inhibitors of lower molecular weight in single patients. Stimulatory activity of 10 000-50 000 MW acting on factor producing cells, but not on colony forming cells directly, was found in all, a variable stimulator eluting with the very high MW fraction in single patients. In two patients who achieved complete autologous bone marrow remission after treatment with high dose immunosuppression, Sephadex fractions of serum before treatment and remission serum were simultaneously tested on autologous bone marrow in remission. Inhibitors were detected before treatment and disappeared in remission, stimulators were not detectable before treatment but became strong in remission. It is concluded that the effect of aplastic anaemia serum on haemopoiesis in culture is determined by the balance of inhibitors and stimulators on both haemopoietic and CSA/BPA producing cells.

Haematopoietic stimulators in the serum of patients with severe aplastic anaemia

Recent studies on sera from patients with aplastic anaemia show it to contain both stimulators and inhibitors of granulopoiesis. We have examined the serum of patients with aplastic anaemia in a short-term liquid culture system of human bone marrow which permits CFU-C proliferation. Increases in CFU-GM numbers over control values were observed with aplasia sera. All sera produced increased megakaryopoiesis, but no alteration in growth of the fibroblasts and macrophages of the adherent stromal layer. With one exception the sera had no significant direct colony stimulating activity when assayed in agar culture, but increased colony numbers were observed when the sera was incorporated into a sub-optimal feeder layer of peripheral blood leucocytes. When aplastic serum was added to adherent cell-depleted liquid cultures, the CFU-C stimulating property was lost, but increased megakaryopoiesis still occurred. These results indicate the presence of a direct-acting thrombopoietin and an indirect-acting stimulator of CFU-C proliferation in the serum of patients with aplastic anaemia, which may be related to the pathophysiology of the condition.

Serum inhibitors in aplastic anaemia

To study the frequency and clinical importance of serum factors inhibiting CFU-c in patients with aplastic anaemia, sera from 21 patients were analysed. The sera of eight patients showed inhibition of at least one normal bone marrow, but strong and consistent inhibition of two or more normal bone-marrow samples was found in only two cases. In both of these two patients the inhibition disappeared after successful therapy. Fair, but not complete, correlation was found between serum inhibitors and HLA-antibodies, suggesting that at least part of these inhibitors are antibodies directed against HLA-antigens present on myeloid progenitor cells. Serum inhibitors appear to be infrequent in the population of patients with aplastic anaemia seen in our hospital and appear to have no major implications for therapy or outcome of the disease.

Survival of CFU-C in recipient blood after bone marrow transplantation

In six patients undergoing allogeneic bone marrow transplantation granulocyte colony and cluster forming units were detectable in the blood up to 24 hours after intravenous marrow infusion. The mean surviving fraction 30 minutes after the end of the infusion was 0.3 for colonies and 0.42 for total aggregates. CFU-C declined logarithmically with time, but a small secondary rise in blood CFU-C occurred 2--6 hours after the end of the marrow infusion. Three patients were plasma-exchanged immediately before the marrow graft for major donor-recipient ABO incompatibility. The proportion of total groups remaining in the blood at 30 minutes was significantly higher in the plasma-pheresed patients (P = less than 0.05), and the secondary rise in CFU-C was less marked, but no correlation of the blood CFU-C decay curve with the subsequent fate of the graft was observed.

Bone marrow culture in aplastic anemia

Blood and bone marrow granulocyte colony forming units (CFUc) were assayed in 46 patients with aplastic anemia, and the serum was examined for its inhibitory action on normal CFUc growth. All patients showed a gross reduction in colonies and clusters in incidence and absolute number in the bone marrow and blood. Two proliferative abnormalities of CFUc in aplastic anaemia were identified: a significantly higher than normal cluster to colony ratio (P less than 0.05) and a higher than normal ratio of granulocytes to total aggregates in the bone marrow. Eleven out of 34 patients tested had serum inhibitory to normal CFUc. These patients were indistinguishable from the rest on haematological and CFUc culture characteristics, and no correlation between the results of CFUc assay and haematological severity was found. The results suggest that the CFUc is abnormal in aplastic anaemia, the reduction in pool size being related to a failure of self-renewal, but an immunological role in the pathogenesis of aplastic anaemia remains unproven. The close relationship of CFUc incidence to the percentage of granulocyte precursors in the marrow, together with the failure of the CFUc assay to predict clinical severity, limits the practical use of the assay to the confirmation of diagnosis in aplastic anaemia.

Effect of antilymphocyte globulin on granulocyte precursors in aplastic anaemia

Granylocyte colony forming units (CFU-C) were studied in 22 patients with severe aplastic anaemia before and after treatment with antilymphocyte globulin (ALG). Nine patients showed a clinical response to ALG characterized by a rise in the granulocyte count to over I X 10(9)/1 within 30 d. These patients were distinguished in vitro from non-responders by an increase in CFU-C numbers after incubation of bone marrow cells with ALG, and by the presence of inhibitors of normal CFU-C in the serum in six out of seven patients tested. In responding patients bone marrow CFU-C rose while most non-responding patients showed no change or a fall in CFU-C after treatment. In addition in three out of four responding patients examined serum inhibitors disappeared after treatment. The horse ALG used in this study also stimulated normal CFU-C in vitro. This evidence is contrary to the hypothesis that ALG stimulates CFU-C in aplasia by inactivating an abnormal suppressor lymphocyte population. The nature of the stimulation by ALG remains unclear. But in practice the effect of ALG on bone marrow cells and study of CFU-C inhibitors in serum could be used to select patients likely to respond to ALG treatment.