Ronald E. Gress

Guidelines for preventing infectious complications among hematopoietic cell transplantation recipients: a global perspective.

In the past decade, modifications in HCT management and supportive care have resulted in changes in recommendations for the prevention of infection in HCT patients. These changes are fuelled by new antimicrobial agents, increased knowledge of immune reconstitution, and expanded conditioning regimens and patient populations eligible for HCT. Despite these advances, infection is reported as the primary cause of death in 8% of autologous HCT patients and 17 – 20% of allogeneic HCT recipients [3]. The major changes in this document, including changes in recommendation ratings, are summarized here. The organization of this document is similar to the previous guidelines. Specifically, the prevention of exposure and disease among pediatric and adult autologous and allogeneic HCT recipients is discussed. The current recommendations consider myeloablative and reduced intensity conditioning for allogeneic HCT similarly since data on infectious complications following reduced intensity conditioning compared to myeloablative conditioning are sparse [4–7]. However, increased information regarding post-transplant immune recovery highlighting differences between myeloablative and reduced intensity HCT are included. The sections of the document have been re-arranged in an attempt to follow the time course of potential infectious risks for patients receiving HCT. Following the background section, information on hematopoietic cell product safety is provided. The subsequent sections discuss prevention of infection by specific micro-organisms. Following organism-specific information, the sections then discuss means of preventing nosocomial infections as well as “do’s and don’ts” for patients following discharge post-transplant. Finally, information on vaccinations is provided. This will hopefully allow the reader to follow the prevention practices needed from the time a donor is selected until the patient regains immune competence. Several topics are new or expanded from the prior document (Table 2). These include information on multiple organisms which were previously not discussed but have seemingly become more clinically relevant in HCT patients over the past decade. Data, and where possible, recommendations are provided regarding the following organisms that were not included in the previous document: Bordetella pertussis; the polyomaviruses BK and JC; hepatitis A, B, and C viruses; human herpesviruses 6, 7, and 8; human metapneumovirus; human immunodeficiency virus; tuberculosis; nocardiosis; malaria; and leishmaniasis. In recognition of our global society, several organisms are discussed that may be limited to certain regions of the world. Included in that section are also those infections that may be ubiquitous but occur infrequently, such as Pneumocystis jiroveci and Nocardia. Table 2 Summary of Changes compared to the Guidelines published in 2000 [1]. Several other changes should be noted. For bacterial infections, these guidelines now recommend quinolone prophylaxis for patients wth neutropenia expected to last as least 7 days (BI). Additionally, the recommendations for contact precautions (AIII), vaccination (BI), and prophylaxis patients with GVHD (AIII) against Streptococcus pneumoniae have been strengthened. The subsection on central line associated blood stream infections is now in the bacterial section. The vaccination section has been dramatically expanded. Changes include the recommendations for PCV rather than PPSV-23 for pneumococcal vaccination, starting some vaccinations earlier post-transplant, and the addition of recommendations for Varivax, HPV vaccine, and (the non-use of) Zostavax vaccine are included. Two additional appendices were added to provide information on desensitization to sulfa drugs and visitor screening questionnaires. Finally, the dosing appendix has merged both adult and pediatric dosing and provides recommendations for several newer antimicrobial agents that were not previously available. In summary, the changes and expansion to this document reflect the growing body of literature detailing infectious complications in HCT patients.

Thymic output generates a new and diverse TCR repertoire after autologous stem cell transplantation in multiple sclerosis patients

Clinical trials have indicated that autologous hematopoietic stem cell transplantation (HSCT) can persistently suppress inflammatory disease activity in a subset of patients with severe multiple sclerosis (MS), but the mechanism has remained unclear. To understand whether the beneficial effects on the course of disease are mediated by lympho-depletive effects alone or are sustained by a regeneration of the immune repertoire, we examined the long-term immune reconstitution in patients with MS who received HSCT. After numeric recovery of leukocytes, at 2-yr follow-up there was on average a doubling of the frequency of naive CD4+ T cells at the expense of memory T cells. Phenotypic and T cell receptor excision circle (TREC) analysis confirmed a recent thymic origin of the expanded naive T cell subset. Analysis of the T cell receptor repertoire showed the reconstitution of an overall broader clonal diversity and an extensive renewal of clonal specificities compared with pretherapy. These data are the first to demonstrate that long-term suppression of inflammatory activity in MS patients who received HSCT does not depend on persisting lymphopenia and is associated with profound qualitative immunological changes that demonstrate a de novo regeneration of the T cell compartment.

IL-7 administration to humans leads to expansion of CD8+ and CD4+ cells but a relative decrease of CD4+ T-regulatory cells

Lymphopenia is a serious consequence of HIV infection and the administration of cancer chemotherapeutic agents. Although growth factors can be administered to patients to increase circulating neutrophils, there is no effective method to stimulate CD8+ lymphocyte production in humans, in vivo. This report is the first to describe the administration of recombinant interleukin-7 to humans and demonstrates the ability of this cytokine to mediate selective increases in CD4+ and CD8+ lymphocytes along with a decrease in the percentage of CD4+ T-regulatory cells. These studies suggest an important role for interleukin-7 in the treatment of patients with lymphopenia.

Donor-derived CD19-targeted T cells cause regression of malignancy persisting after allogeneic hematopoietic stem cell transplantation

New treatments are needed for B-cell malignancies persisting after allogeneic hematopoietic stem cell transplantation (alloHSCT). We conducted a clinical trial of allogeneic T cells genetically modified to express a chimeric antigen receptor (CAR) targeting the B-cell antigen CD19. T cells for genetic modification were obtained from each patients alloHSCT donor. All patients had malignancy that persisted after alloHSCT and standard donor lymphocyte infusions (DLIs). Patients did not receive chemotherapy prior to the CAR T-cell infusions and were not lymphocyte depleted at the time of the infusions. The 10 treated patients received a single infusion of allogeneic anti-CD19-CAR T cells. Three patients had regressions of their malignancies. One patient with chronic lymphocytic leukemia (CLL) obtained an ongoing complete remission after treatment with allogeneic anti-CD19-CAR T cells, another CLL patient had tumor lysis syndrome as his leukemia dramatically regressed, and a patient with mantle cell lymphoma obtained an ongoing partial remission. None of the 10 patients developed graft-versus-host disease (GVHD). Toxicities included transient hypotension and fever. We detected cells containing the anti-CD19-CAR gene in the blood of 8 of 10 patients. These results show for the first time that donor-derived allogeneic anti-CD19-CAR T cells can cause regression of B-cell malignancies resistant to standard DLIs without causing GVHD.

Harnessing the biology of IL-7 for therapeutic application.

Interleukin-7 (IL-7) is required for T cell development and for maintaining and restoring homeostasis of mature T cells. IL-7 is a limiting resource under normal conditions, but it accumulates during lymphopaenia, leading to increased T cell proliferation. The administration of recombinant human IL-7 to normal or lymphopenic mice, non-human primates and humans results in widespread T cell proliferation, increased T cell numbers, modulation of peripheral T cell subsets and increased T cell receptor repertoire diversity. These effects raise the prospect that IL-7 could mediate therapeutic benefits in several clinical settings. This Review summarizes the biology of IL-7 and the results of its clinical use that are available so far to provide a perspective on the opportunities for clinical application of this cytokine.

Pathways of T-cell regeneration in mice and humans : implications for bone marrow transplantation and immmunotherapy

Summary: Much of our understanding of the immunobiology of bone marrow transplantation (BMT) has come from studies in young adult mice reconstituted with T‐cell‐depleted bone marrow after lethal irradiation. Recent evidence indicates, however, that the applicability of conclusions drawn from this model to human BMT may be limited. While mice retain essentially normal thymic function well past sexual maturity, humans show significant age‐related declines in thymic function age‐early in life. Therefore, thymic‐deficient mice may provide a more accurate model for study of the immunobiology of BMT T‐cell regeneration in thymic‐deficient mice occurs primarily via antigen‐driven expansion of mature peripheral T cells resulting m limited immune competence due to quantitative deficiencies in T‐cell number and severe restriction in the diversity of the regenerated T‐cell receptor (TCR) repertoire. Similarly, immune reconstitution in adult humans after BMT is marked by quantitative T‐cell deficiencies, especially in the CD4+ subset, and loss of TCR diversity. Taken together, prevailing evidence suggests that thymic function is suboptimal in most BMT recipients, and that thymic‐independent pathways of T‐cell regeneration are generally limited in their ability to restore host immune competence. New strategies to enhance thymic function in man after BMT would hold great therapeutic potential.

T-cell regeneration: all repertoires are not created equal

Abstract The importance of the thymus for T-cell development is a central tenet of modern immunology, but thymic-independent T-cell generation has also been described. Recent human studies have shown that the balance between thymic-dependent and thymic-independent pathways of T-cell regeneration is primarily determined by age, and that thymic-independent pathways are generally inadequate for restoration of host immunocompetence.

Thymic aging and T-cell regeneration

Summary: Studies of Tcell regeneration using animal models have consistently shown the importance of the thymus for T‐cell regeneration. In humans, recent studies have shown that declines in thymic T cell regenerative capacity begins relatively early in life, resulting in a limited capacity for T‐cell regeneration by young adulthood. As a result, adult humans who experience profound Tcell depletion regenerate T cells primarily via relatively inefficient thymic‐independent pathways, resulting in prolonged CD4 depletion, CD4+ and CDS+ subset alterations, limited TCR repertoire diversity and a propensity for activation induced cell death. These limitations in T‐cell regeneration have significant clinical implications in the setting of HIV infection and bone marrow transplantation and may also contribute to immunologic abnormalities associated with normal aging. While the mechanisms responsible for thymic aging are not well under stood, current evidence suggests that changes within the thymus itself are primary, while age‐related changes in marrow T‐cell progenitors and inhibitory factors within the extrathymic host milieu contribute to a lesser extent. The development of therapies which can reverse thymic aging are critical for improving outcome in clinical settings of T‐cell depletion, and could potentially improve immunologic function in normal aged hosts.

Tumor-Evoked Regulatory B Cells Promote Breast Cancer Metastasis by Converting Resting CD4+ T Cells to T-Regulatory Cells

Pulmonary metastasis of breast cancer requires recruitment and expansion of T-regulatory cells (Treg) that promote escape from host protective immune cells. However, it remains unclear precisely how tumors recruit Tregs to support metastatic growth. Here we report the mechanistic involvement of a unique and previously undescribed subset of regulatory B cells. These cells, designated tumor-evoked Bregs (tBreg), phenotypically resemble activated but poorly proliferative mature B2 cells (CD19(+) CD25(High) CD69(High)) that express constitutively active Stat3 and B7-H1(High) CD81(High) CD86(High) CD62L(Low) IgM(Int). Our studies with the mouse 4T1 model of breast cancer indicate that the primary role of tBregs in lung metastases is to induce TGF-β-dependent conversion of FoxP3(+) Tregs from resting CD4(+) T cells. In the absence of tBregs, 4T1 tumors cannot metastasize into the lungs efficiently due to poor Treg conversion. Our findings have important clinical implications, as they suggest that tBregs must be controlled to interrupt the initiation of a key cancer-induced immunosuppressive event that is critical to support cancer metastasis.

Autoimmunity associated with TGF-beta1-deficiency in mice is dependent on MHC class II antigen expression.

The progressive inflammatory process found in transforming growth factor beta1 (TGF-beta1)-deficient mice is associated with several manifestations of autoimmunity, including circulating antibodies to nuclear antigens, immune complex deposition, and increased expression of both class I and class II major histocompatibility complex (MHC) antigens. The contribution of MHC class II antigens to the genesis of this phenotype has been determined by crossing the TGF-beta1-null [TGF-beta1(-/-)] genotype into the MHC class II-deficient [MHC-II(-/-)] background. Mice homozygous for both the TGF-beta1 null allele and the class II null allele [TGF-beta1(-/-);MHC-II(-/-)] are without evidence of inflammatory infiltrates, circulating autoantibodies, or glomerular immune complex deposits. Instead, these animals exhibit extensive extramedullary hematopoiesis with progressive splenomegaly and adenopathy, surviving only slightly longer than TGF-beta1(-/-);MHC-II(+/+) mice. The role of CD4+ T cells, which are also absent in MHC class II-deficient mice, is directly demonstrated through the administration of anti-CD4 monoclonal antibodies in class II-positive, TGF-beta1(-/-) mice. The observed reduction in inflammation and improved survival emphasize the significance of CD4+ cells in the pathogenesis of the autoimmune process and suggest that the additional absence of class II antigens in TGF-beta1(-/-);MHC-II(-/-) mice may contribute to their extreme myeloid metaplasia. Thus, MHC class II antigens are essential for the expression of autoimmunity in TGF-beta1-deficient mice, and normally may cooperate with TGF-beta1 to regulate hematopoiesis.