Graft Rejection and Graft Failure

Graft failure is defined as the failure to establish hematopoietic engraftment (primary graft failure) or loss of an established graft (secondary graft failure). This is defined as granulocytes failing to recover to > 0.5 × 10⁹/L or falling below this level for ≥ 3 days after initial recovery. Graft failure after autologous transplant occurs rarely and is most often related to infusion of an inadequate number of viable stem cells. Purging techniques which may injure or reduce the numbers of hematopoietic stem cells increase the risk of graft failure. It is recommended that an untreated, autologous backup marrow or peripheral blood stem cell collection be stored; this backup collection can be infused to rescue patients if poor hematologic recovery or graft failure occurs.

Graft failure after allogeneic transplantation is most commonly due to immunologic rejection. Graft rejection is caused by host-derived cytotoxic T lymphocytes or NK cells directed against donor hematopoietic cells.^103,104 With current regimens, rejection occurs in fewer than 2% of transplants from an HLA-identical sibling. The risk is increased in recipients of HLA-mismatched or matched unrelated donor transplants.^39,105,106 Donor CD8+ T lymphocytes provide a graft-facilitating effect, and T lymphocyte depletion from the allogeneic graft increases the risk of graft failure.^107,108 Other accessory cells with graft-facilitating activity also exist.¹⁰⁹ Infusion of a larger number of stem cells⁴² and increasing the myeloablative and immunosuppressive intensity of the preparative regimen⁴¹ enhances engraftment.

Graft failure or poor graft function may be caused by administration of myelosuppressive drugs, graft-versus-host disease, and infections in the early post transplant period. Ganciclovir, given for prevention or treatment of cytomegalovirus infections, is the most common drug producing graft failure; this is generally reversible when the drug is discontinued. Trimethoprim-sulfamethoxazole given to prevent Pneumocystis carinii infections is modestly myelosuppressive and only rarely produces graft failure. Cytomegalovirus,¹¹⁰ parvovirus,¹¹¹ human herpesvirus 6,¹¹² and mycobacterial and fungal infections may also compromise the graft. Poor engraftment may also result from microenvironment or marrow stroma dysfunction related to the patient's underlying disease or prior therapy.

Graft failure that is not due to rejection can often be successfully treated with growth factors G-CSF or GM-CSF¹¹³ or second hematopoietic stem cell infusion from the same donor or an alternative donor.

Graft versus Host Disease (GVHD)

Graft-versus-host disease is a major, potentially life threatening complication of allogeneic hematopoietic transplantation. Acute and chronic GVHD are distinct, but interrelated syndromes. Acute GVHD typically occurs within the first 100 days post transplant and results from reactivity of mature donor T lymphocytes present in the graft directed against disparate major or minor histocompatibility antigens of the recipient (the host). Chronic GVHD is a syndrome of disordered immune regulation that resembles a number of autoimmune diseases. The classical manifestations of chronic GVHD generally develop between day 80 and 2 years post transplant.

The pathophysiology of acute GVHD involves three phases.¹¹⁴ The first involves conditioning-regimen-related tissue injury resulting in cytokine release, upregulation of HLA molecules, activation of macrophages, and generation of a pro-inflammatory state. In the second phase, alloreactive T cells recognize allogeneic antigens presented on host dendritic cells, become activated, and expand. The third phase involves generation of effector cells and cytokines that produce tissue injury. Acute GVHD requires donor T lymphocytes and recipient antigen-presenting cells to occur.¹¹⁵

Acute GVHD involves the skin, gastrointestinal (GI) tract, and liver as the primary target tissues. The hematopoietic and immune systems are also involved. It is unclear why other tissues are not directly affected by GVHD. A maculopapular rash is usually the first presentation and is typically pruritic and confluent. When severe, generalized erythroderma, bullae and desquamation may occur. Acute GVHD of the liver targets the biliary epithelium and produces cholestatic hepatitis with marked elevation of bilirubin and alkaline phosphatase. Synthetic function is usually preserved early in the course. GVHD can affect the entire GI tract, targeting epithelial cells. GI GVHD characteristically produces secretory diarrhea, abdominal pain, and on rare occasions, ileus. Upper GI GVHD produces nausea, vomiting, and anorexia, all which may occur without lower GI tract or other tissue involvement.¹¹⁶ Conjunctivitis and other ocular manifestations, anemia, and thrombocytopenia may also occur.

The diagnosis of acute GVHD is based on clinical assessment, supported by biopsies of involved tissues.^117,118 The staging and grading of acute GVHD is based on the severity of involvement of the various tissues and is outlined in Table 69-3. In general, grade I is mild and does not require treatment. Grade II is moderate and requires systemic treatment, and grades III and IV are severe and life threatening, respectively. Severe GVHD is associated with a poor prognosis because of direct tissue damage, debilitation, and severe immunodeficiency caused by the GVHD process itself and by its treatment with immunosuppressive drugs.

Table 69-3

Clinical staging and grading of GVHD.

The most important factor predicting the risk of GVHD is HLA disparity between the donor and recipient.^37,119 With current immunosuppressive prophylaxis, acute GVHD occurs in 25% to 50% of patients after transplants from an HLA-identical sibling; this may be related to disparity between minor histocompatibility antigens. A higher incidence, up to 60% to 90% has been reported following transplants from mismatched and unrelated donors. Results are improving for unrelated donor transplantation with the use of more precise molecular histocompatibility typing to identify donors. Older age is associated with an increased incidence of acute and chronic GVHD. Male-related minor histocompatibility antigens, H-Y, are potential targets of GVHD¹²⁰ and sex-mismatched grafts from female donors into male recipients have a higher rate of acute GVHD, particularly if the female donor is sensitized to male antigens by prior pregnancy or blood transfusions.¹²¹ Some studies show a history of herpesviruses infection is associated with an increased risk of GVHD.¹²² Less intensive, nonmyeloablative conditioning regimens may also limit the severity of GVHD, presumably due to the limitation of the pro-inflammatory phase that facilitates development of GVHD.⁵⁰

Pharmacologic immunosuppression is generally administered for the first six months post transplant to reduce the incidence and severity of GVHD. The current standard of care combines either cyclosporine or tacrolimus with a short course of methotrexate.^123–125 Cyclosporine and tacrolimus prevent activation of T cells, whereas methotrexate targets proliferating T cells that were activated at the early post transplant phase by host antigens. Addition of corticosteroids is the first line of therapy in patients who develop acute GVHD. Approximately half of patients have a sustained response¹²⁶ and the steroid dose can be gradually tapered off. Steroid-resistant GVHD has an unfavorable prognosis although 30% to 40% of the patients will respond to a second line therapy such as antithymocyte globulin.¹²⁷ The prognosis is best for GVHD limited to the skin. Acute GVHD involving the liver or multiple organs has a poorer prognosis than other sites. Newer investigational agents for treatment of acute GVHD include monoclonal anti-T-cell antibodies, sirolimus, and a number of investigational cytokine inhibitors.

The most effective method for prevention of GVHD is depletion of T lymphocytes from the graft.²² This approach has not been shown to improve survival in HLA-matched sibling or matched unrelated donor transplants due to increased risk of graft failure, relapse, and opportunistic infections. Transplantation from haploidentical donors has a very high risk of acute GVHD, and the best results have been achieved using T-cell depleted transplants. Post transplant immunosuppressive therapy is not required to prevent GVHD if < 10⁵ T cells/kg are infused for HLA-matched sibling transplants, and < 10⁴ T cells/kg for HLA-mismatched cases.

Chronic GVHD is a related syndrome affecting 25% to 60% of recipients of allogeneic transplantation who survive more than 6 months after transplant.¹²⁸ It most often occurs between 80 and 200 days after transplant, but the onset may be delayed to the second year. Chronic GVHD is more common in older patients and in patients with prior acute GVHD although approximately one third of affected patients have a de novo presentation without prior acute GVHD.^128,129 Chronic GVHD may be more prevalent after transplants with peripheral blood stem cells than with marrow transplantation.¹³⁰

Chronic GVHD has protean clinical manifestation similar to those seen in several autoimmune disorders such as progressive systemic sclerosis, Sjögren syndrome, and primary biliary cirrhosis.¹³¹ It is a syndrome of immune dysregulation with generation of autoreactive T cells directed against shared MHC determinant and production of autoantibodies. Chronic GVHD is associated with thymic dysfunction and failure of the thymus to delete autoreactive cells and induce tolerance. Chronic GVHD is associated with profound immunosuppression and the major risk to the patients relates to high incidence of opportunistic infections.

Chronic GVHD most frequently involves the skin, liver, oral cavity, and eyes. Skin involvement consists of erythema, hyperkeratosis, and desquamation. Its onset is often insidious with gradual thickening and tightness of the subcutaneous tissues and limitation of joint flexibility. Additional symptoms include sicca syndrome with dry eyes, dry mouth, and lichenoid changes in the mouth. Liver involvement is characterized by cholestatic changes. Bronchiolitis obliterans may occur without other major manifestations of chronic GVHD. Intestinal involvement with anorexia, dysphagia, malabsorption, and wasting may occur. Polymyositis, serositis, and autoimmune manifestation occur rarely. Secondary infections are common causes of morbidity and mortality, and antimicrobial prophylaxis is warranted. Chronic GVHD may become a chronic debilitating disease affecting quality of life and remains the major determinant of late transplant-related morbidity. Chronic GVHD is classified as “limited” if only minor skin or liver involvement occurs, or “extensive” if there is diffuse involvement of the skin or multiple organs or when the liver histology indicates advanced changes. Progressive onset of extensive chronic GVHD from acute GVHD and the presence of thrombocytopenia are poor prognostic factors.¹³²

Corticosteroids are the first line of therapy for chronic GVHD.¹³³ The chronic nature of this syndrome requires long-term therapy for at least 6 to 9 months, using the lowest steroid doses which control symptoms. Alternate day dosage may be preferable to minimize the complications resulting from chronic steroid therapy. Cyclosporine or tacrolimus may be used in combination with corticosteroids in high-risk patients.^134–136 Combinations of immunosuppressive agents may improve control of the direct manifestations of chronic GVHD, but they increase the risk of infectious morbidity and mortality. Mycophenolate mofetil has some efficacy and can be employed as a steroid sparing agent.^137,138

Regimen-Related Toxicity

Myeloablative preparative regimens used to cytoreduce the malignancy approaches the limit of tolerance for several tissues. The gastrointestinal tract, lungs and liver are the most susceptible to toxic damage, but severe toxicity may also involve the heart, bladder, nervous system, and other tissues. The actual risk for toxicity varies among regimens, is related to the toxicity profiles of the involved agents and is affected by coexisting organ dysfunction, the effects of the diseases and prior therapy, and infections. Most toxicities are experienced during the first 30 days post transplant, but regimen-related hepatic injury (hepatic veno-occlusive disease), pulmonary toxicity, and neurologic effects may be delayed for several months.

Hematologic complications

Hemolytic reactions may result from ABO blood group incompatibility between the donor and recipient.¹³⁹ The incompatibility may be major when the recipient plasma contains isohemagglutinins against donor red blood cells (RBC) or minor when the donor plasma contains isohemagglutinins against recipient RBC. ABO incompatibility is not a contraindication for allogeneic transplant. Red blood cells should be removed from the donor graft to prevent acute hemolytic reaction in cases with major ABO incompatibility and plasma should be removed in pairs with minor ABO incompatibility.

Thrombotic thrombocytopenic purpura (TTP) may occur after hematopoietic transplantation and is more common after allogeneic than autologous transplants.¹⁴⁰ Factors implicated in initiating endothelial injury include chemotherapeutic agents, irradiation, cyclosporine and tacrolimus, cytomegalovirus (CMV) and fungal infections, and cytokine-release syndromes. TTP occurring post autologous or allogeneic hematopoietic transplantation has a poor prognosis. Treatment with plasma exchange results in response in some patients.^141,142

Immunodeficiency and Infections

Recipients of hematopoietic transplants have a severe immunodeficiency involving both T and B-cells.^143–145 Intensive preparative regimens ablate the host immune system. Myeloid cells, macrophage/monocytes, and lymphocytes are subsequently produced from precursor cells present in the graft. The most profound abnormalities occur within the first 6 months followed by slow recovery over the first year.¹⁴⁶ HLA-mismatched or unrelated donor transplants have a more severe immunodeficiency and risk for opportunistic infections, particularly if T-cell depletion is used to prevent GVHD.¹⁴⁷ Recipients of autologous and syngeneic transplants also have a period of immunodeficiency, but their recovery may be more rapid and post transplant infections may be less frequent and severe than after allogeneic transplantation. Patients with acute and chronic GVHD have a profound immunodeficiency state for prolonged periods and are highly susceptible to unusual infections.¹⁴⁸ Recipients of hematopoietic transplants may be susceptible to unusual opportunistic infections and also to acute overwhelming infections. Prophylactic strategies against an array of potential infections and rapid recognition and treatment of infections are an essential part of successful management of transplant recipients.¹⁴⁹ Immunoglobulin replacement therapy should be considered in patients with documented immunoglobulin deficiency. Re-vaccinations should be performed upon immune recovery and are typically carried out one year post transplant.¹⁵⁰ Isolation measures and especially meticulous hand-washing are important in prevention of nosocomial acquisition of infections.

Posttransplant lymphoproliferative disease (PTLD) is a life-threatening complication of allogeneic transplantation.¹⁵¹ It is more prevalent in recipients of T-cell depleted marrow grafts, transplants from unrelated donors, and in patients with GVHD, and especially those treated with aggressive immunosuppressive treatment including antithymocyte globulin (ATG). PTLD in hematopoietic transplant recipients arises from the transformation of donor-derived B lymphocytes by Epstein-Barr virus (EBV) infection. Patients who are seronegative against EBV prior to transplant may develop PTLD early in the course due to primary EBV infection, and the disease may be rapidly progressive. Seropositive patients may develop a more indolent form as a late complication of prolonged immunosuppression. PTLD presents with systemic symptoms, adenopathy, and frequently with extranodal lesions in the GI tract, liver, and central nervous system (CNS). Treatment includes withdrawal of immunosuppression and administration of the antiCD20 monoclonal antibody, rituximab. Cellular therapy with donor lymphocyte infusion, at relatively low cell numbers, have dramatic results in controlling PTLD.¹⁵² More recently methods have been developed to generate EBV-specific cytotoxic lymphocytes for the treatment of this complication.¹⁵³ Patients with increasing levels of EBV deoxyribonucleic acid are at highest risk for lymphoproliferative disease and are candidates for preemptive immunotherapy.¹⁵⁴

Late effects

Late complications of hematopoietic transplantation include delayed effects of high- dose therapy, indolent infections, transfusion-related complications, and chronic GVHD. Late toxicity of high-dose therapy can produce cataracts, pulmonary fibrosis, dental abnormalities, hypothyroidism and hypogonadism, growth retardation, osteoporosis, and avascular necrosis of the hip or other bones.^128,155,156 Permanent sterility occurs in most patients.

There is an increased risk of solid and hematologic secondary tumors after hematopoietic transplantation.^157,158 Solid tumors, mostly head and neck cancers, squamous cell carcinomas, melanomas, and brain and thyroid cancers are more common in recipients of TBI-containing regimens and the cumulative incidence is up to 7% at 15 years. Myelodysplasia and secondary leukemia occur more commonly after autologous transplant, occurring in 4% to 18% of patients within 2.5 to 8.5 years of transplant.^159,160 There is data to suggest that myelodysplasia is associated more with extensive prior therapy than with the high-dose chemotherapy given prior to the transplant.