S. Slavin

Allograft Tolerance after Total Lymphoid Irradiation (TLI)

The ability to induce permanent and specific transplantation tolerance in neonatal mice was first reported by Medawar and his colleagues {Medawar 1953, Billingham & Brent 1956) more than 25 years ago. Since then, several models of tolerance induction in adult laboratory animals have been developed (Binz & Wigzell 1976, Muller-Rucholtz et al. 1976, Von Boehmer et al. 1976, Yunis et ai. 1976), but as yet none have had successful clinical application. During the past several years, we developed a regimen for the induction of transplantation tolerance which allows for the permanent survival of BM, skin and heart allografts in both inbred and outbred adult animals which differ at the major histocompatibility genetic region. The tolerization regimen is based upon the use of total lymphoid irradiation (TLI), a radiotherapy technique which has been used to treat lymphoid malignancies in humans (Kaplan 1972). TLI has few severe side effects, and the mortality rate associated with this procedure is negligible (Kaplan 1972). We review here the essential features of our experimental findings, and suggest that this regimen merits further investigation with regard to applicability to clinical bone marrow and organ transplantation.

Effect of total lymphoid irradiation (TLI) on the primary and secondary antibody response to sheep red blood cells

Abstract The effect of total lymphoid irradiation (TLI) on the primary and secondary hemagglutinin response to sheep red blood cells (SRBC) was studied in BALB/c mice. The primary response was eliminated for 1 month and began to return by Day 44. The latter response was IgM, and the IgG response did not return until approximately 200 days after TLI. The prolonged immunosuppression required inclusion of the thymus in the radiation field. Mice treated with single-dose whole-body irradiation (WBI) regained a normal IgG response within 28 days after irradiation. Immunization of mice prior to treatment with TLI or WBI resulted in a vigorous IgG response when mice were boosted 1 month after irradiation.

The treatment of intractable rheumatoid arthritis with lymphoid irradiation

Abstract Subdisphragmatic lymphoid radiation was used as an alternative to cytotoxic drug therapy to treat six patients with progressive erosive rheumatoid arthritis. All were previously unresponsive to conventional therapy. Radiation (4,000 rad) was given to subdispbragmatic lymphoid tissues in fractionated doses of 150–250 rod each. Three of the six patients demonstrated long-lasting clinical improvement with a decrease in synovitis and morning stiffness and an increase in joint function. All six patients showed a profound depression in the peripheral blood lymphocyte count which persisted for at least six months. The irradiation was well tolerated; there have been no serious complications due to radiotherapy with follow-up ranging from 13 to 36 months. The substantial efficacy in some patients and the lack of severe toxicity in all suggests that radiotherapy deserves further study as an alternative to cytotoxic drugs in the treatment of rheumatoid arthritis.

Long-term effects of splenectomy on immunocompetent cells of adult mice☆

Abstract The long-term effects of adult splenectomy on immunocompetent cells was studied in BALB/c mice during an observation period of 600 days following splenectomy in comparison to age-matched controls. The percentage and absolute number of circulating Thy 1.2-positive (T) cells diminished gradually, reaching about 50% of the level of T cells in age-matched controls, with a concomittant increase in the proportion of Ig-positive (B) cells. The in vitro response of peripheral blood lymphocytes (PBL) to T-cell mitogens showed a 60% decrease of [3H]TdR uptake following phytohemagglutinin stimulation without a significant impairment of the responsiveness to concanavalin A. Alloreactivity of PBL was unaltered by splenectomy since both the in vitro reactivity of PBL to allogeneic cells using mixed leukocyte reaction, and the in vivo assay, measuring a first set skin allograft survival, were similar to those observed in age-matched controls. Studies on the humoral antibody responsiveness to sheep red blood cells (SRBC) indicated a diminished primary, and normal secondary anti-SRBC responses in splenectomized mice. No IgG response was detectable in mice primed with SRBC starting at 160 days following splenectomy, whereas normal IgG titers were observed following SRBC boost in splenectomized mice. We conclude that the spleen seems to play a regulatory role on some immune functions during adult life in mice.

In-vitro T cell mediated function in patients with active rheumatoid arthritis.

In-vitro synthesis of peripheral blood lymphocytes from patients with rheumatoid arthritis was measured after stimulation with phytohaemagglutinin (PHA) in a short-term, serum-free culture system. Diminished responses were found in 16 out of 17 consecutive patients with active disease. Normal PHA responsiveness was recovered by assaying Ficoll-Hypaque isolated E rosette forming cells in serum-free medium, indicating basically normal T cell function in RA. Preincubation of normal peripheral blood lymphocytes (or isolated E rosette forming cells) with sera obtained from patients with active RA for 30 minutes at 4 degrees C or 37 degrees C blocked PHA responsiveness in 34 out of 43 tests. This suggests that serum blocking factors may be responsible for reduced T cell reactivity in RA.

Mechanisms of Transplantation Tolerance to Allogeneic Bone Marrow Cells Following Total Lymphoid Irradiation (TLI)

The lymphocytes, the mediators of cellular events that lead to subsequent allograft rejection, are very radiosensitive, being particularly vulnerable to irradiation during interphase. Nevertheless, sublethal doses of whole body irradiation (WBI) cannot be used as the sole agent for immunosuppression for prevention of allograft rejection due to quick recovery of lymphocyte number and function following WBI. The WBI dose required to ensure engraftment of bone marrow (BM) or organ allografts is intolerable due to irreversible detrimental effects on radiosensitive organs like the BM, the gastrointestinal tract and the lungs. Fractionated, high dose total lymphoid irradiation (TLI) was originally designed to ensure maximal lymphoid depletion and avoiding unnecessary exposure of nonlymphoid organs, using selective ports of irradiation directed to the lymphoid organs.

IMMUNOSUPPRESSION AND PERMANENT TRANSPLANTATION TOLERANCE ACROSS MAJOR HISTOCOMPATIBILITY BARRIERS FOLLOWING TOTAL LYMPHOID IRRADIATION

Publisher Summary This chapter discusses the immunosuppression and permanent transplantation tolerance across major histocompatibility barriers following total lymphoid irradiation. Bone marrow (BM) transplantation presents one of the most complicated problems in both clinical and experimental transplantation immunobiology. Successful allogeneic BM transplantation requires the establishment of initial engraftment, prevention of graft rejection, and avoiding or overcoming graft versus host disease (GVHD), which is a frequent lethal complication. A new approach to BM and transplantation across major histocompatibility barriers with induction of permanent and specific tolerance to donor-type alloantigens in different animal models using fractionated high dose total lymphoid irradiation has recently been developed. Two critical features of total lymphoid irradiation (TLI) used in animals and in man are the shielding of radiosensitive nonlymphoid organs with lead and the high dose of irradiation achieved by well-tolerable small daily fractions of 200 rads each.