A Critical Role for CD48 Antigen in Regulating Alloengraftment and Lymphohematopoietic Recovery After Bone Marrow Transplantation

Blood ◽  
1998 ◽  
Vol 92 (11) ◽  
pp. 4453-4463 ◽  
Author(s):  
Bruce R. Blazar ◽  
Patricia A. Taylor ◽  
Angela Panoskaltsis-Mortari ◽  
Hideo Yagita ◽  
Jonathan S. Bromberg ◽  
...  
Keyword(s):  
Bone Marrow ◽  
T Cells ◽  
Bone Marrow Transplantation ◽  
T Cell ◽  
Marrow Transplantation ◽  
Cytotoxic T Lymphocyte ◽  
Critical Role ◽  
Cell Functions ◽  
Hematopoietic Recovery ◽  
Delayed Recovery

Abstract The binding of CD2, present on T cells, to its counterreceptor CD48 facilitates adhesion, signaling, alloantigen-induced cytokine production, and cytotoxic T-lymphocyte responses. Because these T-cell functions have been implicated in graft-versus-host disease (GVHD) pathogenesis, we have analyzed the effects of the CD2:CD48 pathway on GVHD mediated by CD4+ and CD8+ T cells infused into sublethally irradiated recipients. CD4+ T-cell–mediated, and to a lesser extent, CD8+ T-cell–mediated GVHD was inhibited by CD2 + 48 monoclonal antibody (MoAb) infusion. To assess the effects of combined MoAb infusion on alloengraftment, two different alloengraftment bone marrow transplantation (BMT) models were used. In both, MoAb infusion markedly inhibited alloengraftment and hematopoietic recovery post-BMT. To determine if the adverse effects on lymphohematopoiesis in the allogeneic BMT recipients were caused by an immune or nonimmune mechanism, studies were performed in congenic BMT recipients to preclude an immune mechanism as the cause for delayed recovery post-BMT. MoAb infusion resulted in impaired lymphohematopoietic recovery in congenic BMT recipients and markedly reduced day 12 colony-forming unit–spleen formation in syngeneic BMT recipients, consistent with a nonimmune mediated mechanism. Because the spleen is a site of early hematopoietic recovery post-BMT, studies were performed using adult splenectomized syngeneic BMT recipients. MoAb infusion delayed recovery in both nonsplenectomized and splenectomized recipients post-BMT, indicating that the delayed hematopoietic recovery was not the consequence of an abnormal homing pattern of hematopoietic progenitors to the spleen early post-BMT. CD48 MoAb was necessary and sufficient for the inhibition of GVHD lethality and delayed lymphohematopoietic effects of the combined MoAb regimen. CD48 MoAb was found to induce a profound modulation of CD48 antigen expression on BM cells, suggesting that the CD48 antigen may have an important function in hematopoiesis in the BM compartment. Taken together, these data provide evidence that the CD48 antigen plays a critical role in regulating hematopoiesis in post-BMT.

A Critical Role for CD48 Antigen in Regulating Alloengraftment and Lymphohematopoietic Recovery After Bone Marrow Transplantation

Blood ◽  
1998 ◽  
Vol 92 (11) ◽  
pp. 4453-4463 ◽  
Author(s):  
Bruce R. Blazar ◽  
Patricia A. Taylor ◽  
Angela Panoskaltsis-Mortari ◽  
Hideo Yagita ◽  
Jonathan S. Bromberg ◽  
...  
Keyword(s):  
Bone Marrow ◽  
T Cells ◽  
Bone Marrow Transplantation ◽  
T Cell ◽  
Marrow Transplantation ◽  
Cytotoxic T Lymphocyte ◽  
Critical Role ◽  
Cell Functions ◽  
Hematopoietic Recovery ◽  
Delayed Recovery

The binding of CD2, present on T cells, to its counterreceptor CD48 facilitates adhesion, signaling, alloantigen-induced cytokine production, and cytotoxic T-lymphocyte responses. Because these T-cell functions have been implicated in graft-versus-host disease (GVHD) pathogenesis, we have analyzed the effects of the CD2:CD48 pathway on GVHD mediated by CD4+ and CD8+ T cells infused into sublethally irradiated recipients. CD4+ T-cell–mediated, and to a lesser extent, CD8+ T-cell–mediated GVHD was inhibited by CD2 + 48 monoclonal antibody (MoAb) infusion. To assess the effects of combined MoAb infusion on alloengraftment, two different alloengraftment bone marrow transplantation (BMT) models were used. In both, MoAb infusion markedly inhibited alloengraftment and hematopoietic recovery post-BMT. To determine if the adverse effects on lymphohematopoiesis in the allogeneic BMT recipients were caused by an immune or nonimmune mechanism, studies were performed in congenic BMT recipients to preclude an immune mechanism as the cause for delayed recovery post-BMT. MoAb infusion resulted in impaired lymphohematopoietic recovery in congenic BMT recipients and markedly reduced day 12 colony-forming unit–spleen formation in syngeneic BMT recipients, consistent with a nonimmune mediated mechanism. Because the spleen is a site of early hematopoietic recovery post-BMT, studies were performed using adult splenectomized syngeneic BMT recipients. MoAb infusion delayed recovery in both nonsplenectomized and splenectomized recipients post-BMT, indicating that the delayed hematopoietic recovery was not the consequence of an abnormal homing pattern of hematopoietic progenitors to the spleen early post-BMT. CD48 MoAb was necessary and sufficient for the inhibition of GVHD lethality and delayed lymphohematopoietic effects of the combined MoAb regimen. CD48 MoAb was found to induce a profound modulation of CD48 antigen expression on BM cells, suggesting that the CD48 antigen may have an important function in hematopoiesis in the BM compartment. Taken together, these data provide evidence that the CD48 antigen plays a critical role in regulating hematopoiesis in post-BMT.

scholarly journals Outcome of alloanergized haploidentical bone marrow transplantation after ex vivo costimulatory blockade: results of 2 phase 1 studies

Blood ◽  
2008 ◽  
Vol 112 (6) ◽  
pp. 2232-2241 ◽  
Author(s):  
Jeff K. Davies ◽  
John G. Gribben ◽  
Lisa L. Brennan ◽  
Dongin Yuk ◽  
Lee M. Nadler ◽  
...  
Keyword(s):  
Bone Marrow ◽  
T Cells ◽  
Bone Marrow Transplantation ◽  
T Cell ◽  
Marrow Transplantation ◽  
Viral Infections ◽  
Ex Vivo ◽  
Chronic Gvhd ◽  
Costimulatory Blockade ◽  
Donor T Cells

AbstractWe report the outcomes of 24 patients with high-risk hematologic malignancies or bone marrow failure (BMF) who received haploidentical bone marrow transplantation (BMT) after ex vivo induction of alloantigen-specific anergy in donor T cells by allostimulation in the presence of costimulatory blockade. Ninety-five percent of evaluable patients engrafted and achieved full donor chimerism. Despite receiving a median T-cell dose of 29 ×106/kg, only 5 of 21 evaluable patients developed grade C (n = 4) or D (n = 1) acute graft-versus-host disease (GVHD), with only one attributable death. Twelve patients died from treatment-related mortality (TRM). Patients reconstituted T-cell subsets and immunoglobulin levels rapidly with evidence of in vivo expansion of pathogen-specific T cells in the early posttransplantation period. Five patients reactivated cytomegalovirus (CMV), only one of whom required extended antiviral treatment. No deaths were attributable to CMV or other viral infections. Only 1 of 12 evaluable patients developed chronic GVHD. Eight patients survive disease-free with normal performance scores (median follow-up, 7 years). Thus, despite significant early TRM, ex vivo alloanergization can support administration of large numbers of haploidentical donor T cells, resulting in rapid immune reconstitution with very few viral infections. Surviving patients have excellent performance status and a low rate of chronic GVHD.

scholarly journals Evidence for extrathymic generation of intermediate T cell receptor cells in the liver revealed in thymectomized, irradiated mice subjected to bone marrow transplantation.

1995 ◽  
Vol 182 (3) ◽  
pp. 759-767 ◽  
Author(s):  
K Sato ◽  
K Ohtsuka ◽  
K Hasegawa ◽  
S Yamagiwa ◽  
H Watanabe ◽  
...  
Keyword(s):  
Bone Marrow ◽  
T Cells ◽  
Bone Marrow Transplantation ◽  
T Cell ◽  
T Cell Receptor ◽  
Marrow Transplantation ◽  
Interleukin 2 ◽  
Cell Receptor ◽  
Phenotypic Characterization ◽  
Receptor Cells

In addition to the major intrathymic pathway of T cell differentiation, extrathymic pathways of such differentiation have been shown to exist in the liver and intestine. In particular, hepatic T cells of T cell receptors or CD3 of intermediate levels (i.e., intermediate T cell receptor cells) always contain self-reactive clones and sometimes appear at other sites, including the target tissues in autoimmune diseases and the tumor sites in malignancies. To prove their extrathymic origin and self reactivity, in this study we used thymectomized, irradiated (B6 x C3H/He) F1 mice subjected to transplantation of bone marrow cells of B6 mice. It was clearly demonstrated that all T cells generated under athymic conditions in the peripheral immune organs are intermediate CD3 cells. In the case of nonthymectomized irradiated mice, not only intermediate CD3 cells but also high CD3 cells were generated. Phenotypic characterization showed that newly generated intermediate CD3 cells were unique (e.g., interleukin 2 receptor alpha-/beta+ and CD44+ L-selectin-) and were, therefore, distinguishable from thymus-derived T cells. The precursor cells of intermediate CD3 cells in the bone marrow were Thy-1+ CD3-. The extrathymic generation of intermediate CD3 cells was confirmed in other combinations of bone marrow transplantation, C3H --> C3H and B10.Thy1.1 --> B6.Thy1.2. The generated intermediate CD3 cells in the liver contained high levels of self-reactive clones estimated by anti-V beta monoclonal antibodies in conjunction with the endogenous superantigen minor lymphocyte-stimulating system, especially the combination of B6 --> (B6 x C3H/He) (graft-versus-host-situation).(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Cytogenetic analysis of chimerism and leukemia relapse in chronic myelogenous leukemia patients after T cell-depleted bone marrow transplantation

Blood ◽  
1990 ◽  
Vol 75 (6) ◽  
pp. 1346-1355
Author(s):  
K Offit ◽  
JP Burns ◽  
I Cunningham ◽  
SC Jhanwar ◽  
P Black ◽  
...  
Keyword(s):  
Bone Marrow ◽  
T Cells ◽  
Bone Marrow Transplantation ◽  
T Cell ◽  
Marrow Transplantation ◽  
Myelogenous Leukemia ◽  
Host Cells ◽  
Clinical Relapse ◽  
Cytogenetic Studies ◽  
Ph Chromosome

Serial cytogenetic studies were performed on 64 patients with chronic myelogenous leukemia (CML) after T cell-depleted allogeneic bone marrow transplantation (BMT). Forty patients with CML in chronic phase (CP) received cytoreduction followed by BMT with HLA-matched T cell-depleted allogeneic marrow. The remaining 24 patients were transplanted in second chronic, accelerated, or blastic phase, or received T cell- depleted grafts with a dose of T cells added back. The Y chromosome and autosomal heteromorphisms were used to distinguish between donor and host cells. Mixed hematopoietic chimerism (presence of donor and host cells) was identified in 90% of patients in first CP. The Philadelphia (Ph) chromosome reappeared in 16 of the 40 first CP CML patients. As expected, patients who had detectable Ph chromosome positive cells at any time during the posttransplant period had a high likelihood of subsequent clinical relapse. Transient disappearance of the Ph positive clone was rarely observed, and was followed by reappearance of the Ph chromosome or clinical relapse. A subset of engrafted patients with greater than 25% host cells within 3 months post-BMT had a significantly shorter survival time free of cytogenetic or clinical relapse compared with other patients. In patients who had received donor T cells added to the T cell-depleted graft, there was a higher proportion of complete chimerism. Clonal progression of Ph positive as well as negative cells was observed and may be the result of radiation induced breakage. Serial cytogenetic studies of patients post-BMT can provide useful information regarding the biologic and clinical behavior of CML.

scholarly journals Imbalances within the peripheral blood T-helper (CD4+) and T-suppressor (CD8+) cell populations in the reconstitution phase after human bone marrow transplantation

Blood ◽  
1988 ◽  
Vol 71 (5) ◽  
pp. 1196-1200 ◽  
Author(s):  
A Velardi ◽  
A Terenzi ◽  
S Cucciaioni ◽  
R Millo ◽  
CE Grossi ◽  
...  
Keyword(s):  
Bone Marrow ◽  
T Cells ◽  
Bone Marrow Transplantation ◽  
T Cell ◽  
Peripheral Blood ◽  
Marrow Transplantation ◽  
Allogeneic Bone Marrow Transplantation ◽  
T Cell Subsets ◽  
Allogeneic Bone ◽  
T Helper

Abstract Peripheral blood T cell subsets were evaluated in 11 patients during the reconstitution phase after allogeneic bone marrow transplantation and compared with 11 age-matched controls. The proportion of cells coexpressing Leu7 and CD11b (C3bi receptor) markers was determined within the CD4+ (T-helper) and the CD8+ (T-suppressor) subsets by two- color immunofluorescence analysis. CD4+ and CD8+ T cells reached normal or near-normal values within the first year posttransplant. In contrast to normal controls, however, most of the cells in both subsets coexpressed the Leu7 and CD11b markers. T cells with such phenotype display the morphological features of granular lymphocytes (GLs) and a functional inability to produce interleukin 2 (IL 2). These T cell imbalances were not related to graft v host disease (GvHD) or to clinically detectable virus infections and may account for some defects of cellular and humoral immunity that occur after bone marrow transplantation./

scholarly journals Analysis of T lymphocytes after bone marrow transplantation using monoclonal antibodies

Blood ◽  
1982 ◽  
Vol 60 (3) ◽  
pp. 578-582 ◽  
Author(s):  
R Fox ◽  
R McMillan ◽  
W Spruce ◽  
P Tani ◽  
D Mason
Keyword(s):  
Bone Marrow ◽  
T Cells ◽  
Monoclonal Antibodies ◽  
Bone Marrow Transplantation ◽  
T Cell ◽  
Cell Surface ◽  
Marrow Transplantation ◽  
T Cell Subsets ◽  
Clinically Significant ◽  
Abnormal Ratio

Abstract Using monoclonal antibodies to cell surface antigens and fluorescent cell sorter analysis, we studied peripheral blood lymphocyte subsets after bone marrow transplantation (BMT). In 13 patients studied 3 mo or more after BMT, the ratio of T-cell subsets defined by antibodies OKT4 and OKT8 was reversed (OKT4/OK%8 = 0.7 +/- 0.3) in comparison to normal volunteers or bone marrow donors (ratio OKT4/OKT8 = 1.7 +/- 0.4) (p less than 0.001). This reversed ratio persisted for up to 3 yr after BMT. In contrast to a previous report, presence of an abnormal ratio of T-cell subsets did not correlate with clinically significant graft- versus-host disease (GVHD). In agreement with a previous study, (26% +/- 8%; less than 4% in normals (p less than 0.001) and antibody OKT10 reactive cells (39% +/- 20% versus 10% +/- 4%) (p less than 0.01), suggesting in vivo activation. However, their PBL did not react with antibody B3/25 (antitransferrin receptor), a marker found on normal PBL after in vitro activation by mitogens (BMT patients less than 5%; normal PBL T cells plus PHA 45% +/- 11%). These results demonstrate that BMT patients have: (A) an abnormal ratio of T-cell subsets in the presence or absence of clinically significant GVDH disease so that these measurements were not useful in monitoring patients; (B) an increased number of T cells with cell surface phenotype (OKT8+, Ia+, OKT10+, B3/25-) that is distinct from normals but similar to patients with infectious mononucleosis or acquired hypogammaglobulinemia.

scholarly journals T-cell regeneration after bone marrow transplantation: differential CD45 isoform expression on thymic-derived versus thymic-independent progeny

Blood ◽  
1993 ◽  
Vol 82 (8) ◽  
pp. 2585-2594 ◽  
Author(s):  
CL Mackall ◽  
L Granger ◽  
MA Sheard ◽  
R Cepeda ◽  
RE Gress
Keyword(s):  
Bone Marrow ◽  
T Cells ◽  
Bone Marrow Transplantation ◽  
T Cell ◽  
Marrow Transplantation ◽  
Cell Receptor ◽  
Cell Regeneration ◽  
Thymic Function ◽  
T Cell Progenitors ◽  
Isoform Expression

Abstract To study the source of regenerated T cells after bone marrow transplantation (BMT), lethally irradiated thymectomized and thymus- bearing C57BL/6 (Thy 1.2+) mice were injected with syngeneic T-cell depleted bone marrow (TCD BM) cells and graded numbers of congenic B6/Thy 1.1+ lymph node (LN) cells. LN cell expansion was the predominant source for T-cell regeneration in thymectomized hosts but was minimal in thymus-bearing hosts. Analysis of T-cell receptor (TCR) expression on LN progeny showed a diverse V beta repertoire. Therefore, peripheral T-cell progenitors exist within V beta families, but expansion of these progenitors after BMT is downregulated in the presence of a functional thymus. CD4+ cells derived from BM versus LN in thymus-bearing hosts displayed differential CD44 and CD45 isoform expression. BM-derived cells were primarily CD45RB+CD44lo and LN derived cells were nearly exclusively CD45RB- CD44hi. In thymectomized hosts, BM, host, and LN CD4+ progeny were CD45RB- CD44hi. We conclude that T-cell regeneration via peripheral T-cell progenitors predominates in hosts lacking thymic function and gives rise to T cells that display a “memory” phenotype. In contrast, the ability to generate sizable populations of “naive” type T cells after BMT appears limited to the prethymic progenitor pool and could serve as a marker for thymic regenerative capacity.

scholarly journals Cytogenetic analysis of chimerism and leukemia relapse in chronic myelogenous leukemia patients after T cell-depleted bone marrow transplantation

Blood ◽  
1990 ◽  
Vol 75 (6) ◽  
pp. 1346-1355 ◽  
Author(s):  
K Offit ◽  
JP Burns ◽  
I Cunningham ◽  
SC Jhanwar ◽  
P Black ◽  
...  
Keyword(s):  
Bone Marrow ◽  
T Cells ◽  
Bone Marrow Transplantation ◽  
T Cell ◽  
Marrow Transplantation ◽  
Myelogenous Leukemia ◽  
Host Cells ◽  
Clinical Relapse ◽  
Cytogenetic Studies ◽  
Ph Chromosome

Abstract Serial cytogenetic studies were performed on 64 patients with chronic myelogenous leukemia (CML) after T cell-depleted allogeneic bone marrow transplantation (BMT). Forty patients with CML in chronic phase (CP) received cytoreduction followed by BMT with HLA-matched T cell-depleted allogeneic marrow. The remaining 24 patients were transplanted in second chronic, accelerated, or blastic phase, or received T cell- depleted grafts with a dose of T cells added back. The Y chromosome and autosomal heteromorphisms were used to distinguish between donor and host cells. Mixed hematopoietic chimerism (presence of donor and host cells) was identified in 90% of patients in first CP. The Philadelphia (Ph) chromosome reappeared in 16 of the 40 first CP CML patients. As expected, patients who had detectable Ph chromosome positive cells at any time during the posttransplant period had a high likelihood of subsequent clinical relapse. Transient disappearance of the Ph positive clone was rarely observed, and was followed by reappearance of the Ph chromosome or clinical relapse. A subset of engrafted patients with greater than 25% host cells within 3 months post-BMT had a significantly shorter survival time free of cytogenetic or clinical relapse compared with other patients. In patients who had received donor T cells added to the T cell-depleted graft, there was a higher proportion of complete chimerism. Clonal progression of Ph positive as well as negative cells was observed and may be the result of radiation induced breakage. Serial cytogenetic studies of patients post-BMT can provide useful information regarding the biologic and clinical behavior of CML.

Immunoregulatory Effects of Allogeneic Mixed Chimerism Induced by T-Cell Depleted, Nonmyeloablative Bone Marrow Transplantation on Chronic Inflammatory Arthritis and Autoimmunity Developed in Interleukin-1 Receptor Antagonist-Deficient Mice.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 1277-1277
Author(s):  
Seok-Goo Cho ◽  
Min-Chung Park ◽  
So-Youn Min ◽  
Young-Gyu Cho ◽  
Seok Lee ◽  
...  
Keyword(s):  
Bone Marrow ◽  
T Cells ◽  
Bone Marrow Transplantation ◽  
T Cell ◽  
Marrow Transplantation ◽  
Inflammatory Arthritis ◽  
Interleukin 1 ◽  
Mixed Chimerism ◽  
Control Groups ◽  
Chronic Inflammatory Arthritis

Abstract Objective: To investigate the immunoregulatory effects of allogeneic mixed chimerism induced by T-cell depleted, nonmyeloablative bone marrow transplantation (TCD-NMT) on chronic inflammatory arthritis and autoimmunity developed in interleukin-1 receptor antagonist-deficient (IL-1Ra−/ −) mice. Methods: IL-1Ra−/ − mice (H-2kd) were treated with anti-asialoGM1 Ab, TBI 500 cGy, and TCD-NMT from C57BL/6 mice (H-2kb). Engraftment and chimerism were evaluated on peripheral blood (PB), lymph node, and spleen by multi-color flow cytometry. The severity of arthritis was evaluated by clinical score and histopathology. IgG1 and IgG2a subtype of anti-type II collagen (CII) were measured in PB samples. After T cells were stimulated with CII, ovalbumin, and phytohemagglutinin, T-cell proliferation response and cytokines production (INF-g, TNF-a, IL-10, and IL-17) in culture supernatant were assayed. Results: All the transplanted IL-1Ra mice showed marked improvement of arthritis within 3 weeks after transplantation as well as successful induction of mixed chimerism. Mice in mixed chimerism showed higher level of anti-CII IgG1 and lower level of anti-CII IgG2a and weaker T cell proliferative response than in control groups, such as no-treatment and conditioning only without BM rescue. In mixed chimera, INF-g, TNF-a and IL-17 production from CII-stimulated T cells was significantly suppressed and IL-10 production was significantly increased as compared to the control groups. Conclusion: These observations indicate that the introduction of allogeneic mixed chimerism has a strong immunoregulatroy potential to correct established chronic inflammatory arthritis and autoimmunity originating from dysregulated proinflammatory cytokine network.

Graft-Versus-Host Tolerance in Dogs Following T-Cell Depleted Bone Marrow Transplantation with Absorbed ATG or CD6-Antibody.

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 2338-2338
Author(s):  
Julia Zorn ◽  
Hans Jochem Kolb
Keyword(s):  
Bone Marrow ◽  
T Cells ◽  
Stem Cell ◽  
Bone Marrow Transplantation ◽  
T Cell ◽  
Nk Cells ◽  
Marrow Transplantation ◽  
Graft Versus Host ◽  
Host Tolerance ◽  
Rabbit Complement

Abstract Graft-versus-host disease (GvHD) is the major obstacle of allogeneic stem cell transplantation. Depletion of T-cells from the graft reduces the risk of GvHD, but results in a higher risk of leukemia relapse. Adoptive immunotherapy with donor lymphocyte transfusion (DLT) has been shown to control leukemia in patients after T-cell depleted allogeneic stem cell transplantation. However, GvHD may occur, if DLT is given too early after transplantation. In canine models of DLA-identical and DLA-haploidentical bone marrow transplantation, we compared different methods of T-cell depletion (TCD) and investigated the potential of DLT at different times after transplantation to induce GvHD. T-cell depletion was performed either with absorbed anti-thymocyte globuline (aATG) or with a combination of CD6-antibody and baby rabbit complement. ATG was absorbed with erythrocytes, liver, kidney and spleen for eliminating antibodies against stem cells. CD6-antibody (M-T606) and rabbit complement depleted T-cells effectively without affecting hematopoietic progenitor cells. Unlike aATG, monoclonal CD6-antibody spares natural killer (NK) cells and some CD8-positive cells. Treatment of bone marrow with aATG prevented GvHD in 9 dogs following DLA-identical transplantation. DLT on days 1 and 2 or 21 and 22 induced fatal GvHD in two dogs each. However, it did not induce GvHD when given on days 61 and 62 and later. In DLA-haploidentical bone marrow recipients, non-manipulated marrow produced fatal GvHD in all dogs (n=7), whereas marrow treated with aATG (vol:vol 1:100 and 1:200) produced fatal GvHD in 5 out of 16 dogs only. CD6-depletion prevented GvHD in 3 of 3 DLA-haploidentically transplanted dogs. DLT produced fatal GvHD in one dog each, when given on day 3, 7 or 14 after CD6-depleted haploidentical bone marrow transplantation. However, it produced fatal GvHD in only 2 of 4 dogs transfused on day 20 post grafting. Thus, DLT could be given earlier in DLA-haploidentical animals transplanted with CD6-depleted marrow than in DLA-identical animals transplanted with aATG treated marrow without producing GvHD. These findings support the hypothesis that graft-versus-host tolerance can be induced earlier with grafts not depleted of NK cells. NK cells in the graft may inactivate host dendritic cells necessary for the induction of GvHD. In grafts depleted with aATG, NK cells are depleted as well, because aATG still retains broad specificity despite extensive absorptions. This leaves host DCs unaffected. Transfused donor T-cells encountering this environment will thus be activated which results in severe GvHD. In contrast, monoclonal CD6-antibody spares NK cells, so that donor lymphocytes cannot be activated by host DCs at the time of DLT and thus won’t trigger GvHD. CD6-depletion is the preferred method if adoptive immunotherapy with DLT is planned.

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