Frequencies Of CMV-specific CD8 Research Articles

Investigating the Dynamics of MCMV-Specific CD8+ T Cell Responses in Individual Hosts.

Infection by Cytomegalovirus (CMV) is characterized by the massive expansion and continued maintenance of CMV-specific CD8+ T cells for certain CMV-derived peptides. This phenomenon called “memory inflation" has made CMV a primary target for the generation of T cell based vaccine vectors against various diseases. However, many aspects concerning the generation and maintenance of the inflationary CD8+ T cell response still remain to be resolved. In this study, we combined experimental data and mathematical models to analyze the dynamics of circulatory inflationary CD8+ T cells within individual mice infected by MCMV. Obtaining frequent measurements on the number and frequency of CMV-specific CD8+ T cells up to 70 days post infection, we find that mathematical models assuming differing viral stimuli during acute infection and the inflationary phase provide a better description for the observed dynamics than models relying on similar viral stimuli during both phases. In addition, our analysis allowed a detailed quantification of the different phases of memory inflation within individual mice (1st-expansion - contraction - 2nd expansion/maintenance) indicating remarkable consistency of the timing of these phases across mice, but considerable variation in the size of the individual responses between mice. Our analysis provides a first step toward generating a mechanistic framework for analyzing the generation and maintenance of inflationary CD8+ T cells while accounting for individual heterogeneity. Extending these analyses by incorporating measurements from additional compartments and more prolonged sampling will help to obtain a systematic and quantitative understanding of the factors regulating the process of memory inflation.

Adoptive transfer and selective reconstitution of streptamer‐selected cytomegalovirus‐specific CD8+ T cells leads to virus clearance in patients after allogeneic peripheral blood stem cell transplantation

Cytomegalovirus (CMV) disease constitutes a serious complication after allogeneic stem cell transplantation. For the clearance of CMV, CD8+ T cells are pivotal. Here, the novel streptamer technology was used at good manufacturing practice (GMP) level for adoptive transfer of CMV-specific T cells into acute leukemia patients with recurrent high CMV antigenemia after allogeneic stem cell transplantation. After a single transfusion, the frequency of CMV-specific CD8+CD45RA+CCR7- effector T cells increased dramatically from 0.0% to a maximum of 27.1% of all T cells. These T cells were clearly donor derived and did not stem from intrinsic reconstitution, as demonstrated by analysis of 1) donor chimerism through single-tandem repeats, 2) T-cell receptor excision circles, and 3) Vβ-chain typing by polymerase chain reaction. Clinically, the specific T-cell transfer resulted in a persistent clearance of the CMV antigenemia, which allowed the patients to discontinue toxic antiviral drug therapy without further high-level reactivation of CMV, demonstrating the power of the streptamer technology. Taken together, the streptamer technology offers the advantage of selecting virus-specific CD8+ T cells at GMP level for adoptive T-cell transfer, thus inducing long-lasting specific CD8+ T-cell responses without increasing the risk for graft-versus-host disease.

Human Bone Marrow as a Source of Multifunctional CMV-Specific CD4+ T Cells for Adoptive Cell Therapy.

Introduction Adoptive cell transfer of ex vivo primed and expanded human cytotoxic T lymphocytes (CTLs) has emerged as a promising approach to treat both infectious and malignant diseases in humans. First clinical studies have shown that transfer of Cytomegalovirus (CMV)-specific CD8+ T cells is safe and effective in reconstitution of cellular immunity against CMV disease. Efficacy of adoptive T cell therapy is limited by the numbers of CTLs in vitro and the survival and function after infusion. CD4+ T cells may enhance activity via direct or indirect effector functions (Matloubian 1994 [1]). In this study we have analysed whether bone marrow is superior to peripheral blood for expansion of CMV-specific T cells. Experimental design Paired peripheral blood and bone marrow samples were obtained from patients who underwent total hip arthroplasty. By using two different protocols T cells were expanded in the presence of IL-2 and IL-7 either from bulk culture with exposure of two different peptide pools (IE1 and pp65) or after selection via IFN-γ secretion by stimulation with pp65. CMV specific immune responses were assessed by using multiparameter flow cytometry staining cells for CD3, CD4, CD8, CCR7 and CD45RA and for the cytokines IFN-γ IL-2 and TNF at day 0 and after 10 days of in vitro expansion.Results Similar frequencies of cytokine-producing pp65– and IE1-specific CD4+ and CD8+ T cells were found in unmanipulated paired PB and BM samples. Expansion of CMV-specific T cells from BM resulted in significantly higher frequencies of specific CD4+ T cells than from PB, whereas no difference in frequencies of CMV-specific CD8+ T cells was observed. Interestingly, significantly higher frequencies of BM pp65 and IE1-specific CD4+ T cells were multifunctional, characterized by producing simultaneously IFN-γ, TNF and IL-2 (IE1: BM mean 0.44% ± 0.16; PB mean 0.09% ± 0.05, p=0.031; pp65: BM mean 3.87% ± 2.46; PB mean 1.24% ± 0.90, p=0.031). Expansion of multi-functional CD4+ T cells from BM was observed with both the bulk and selection assay protocol. Both PB and BM CMV-specific CD4+ and CD8+ T cell lines had a predominant CD45RA-CCR7- effector memory phenotype.Conclusions This study implicates the use of human bone marrow as a source for expansion of multifunctional CMV-specific CD4+ T cells. Recent studies in HIV and Leishmania support the crucial role of multifunctional T cells in disease control (Darrah 2007 [2]).

Bone marrow transplantation from a pediatric donor with a high frequency of cytomegalovirus-specific T-cells

A recent study reported that quantitation of cytomegalovirus (CMV)-specific CD8+ T lymphocytes in the graft and monitoring of these T cells might identify hematopoietic stem cell transplantation-recipients at the risk for progressive CMV infection. A 6-year-old girl underwent bone marrow transplantation from an HLA-identical sibling with a very high frequency of CMV specific tetramer-positive CD8+ T-cells. CMV-specific T-cell immunity was prospectively evaluated using a peptide (HLA-A2, NLVPMVATV). Tetramer assay showed that the frequency of CMV-specific CD8+ T cells of the donor in the peripheral blood was 5.3%, higher than average amongst young children. The frequency of CMV-specific CD8+ T cells of the donor in the graft was 3.7% of CD8+ T-cells. Before transplantation, the frequency of CMV specific CD8+ T cells of the recipient was 0.1% in the peripheral blood. Surprisingly, the frequency of CMV specific CD8+ T cells increased up to 30% of CD8+ T-cells at day 27 after transplantation. IFN-gamma enzyme-linked immunospot assay showed the recipient-T cells had strong responses to the A2-specific NLVPMVATV peptide. Although the phenotypic pattern of the CMV-specific T cells of the recipient was different from those of the donor before transplantation, the phenotype of the donor-derived cells retained their original phenotype in the recipient after transplantation. These finding suggested that active transferred immunity from the graft with a high frequency of CMV-specific CTL could induce a rapid reconstitution of CMV-specific T-cell mediated immunity in pediatric HLA-identical allogenetic bone marrow transplantation. The screening of peripheral blood using HLA-peptide tetramer staining might be beneficial to select donors.

FUNCTIONAL CHARACTERIZATION OF CMV-SPECIFIC CD8 T LYMPHOCYTES IN HUMAN LUNG TRANSPLANT RECIPIENTS

P1017 Aims: Human cytomegalovirus (CMV) continues to be a significant cause of morbidity in immunosuppressed lung transplant recipients (LTR), this despite the routine use of prophylactic antiviral therapies. Given the importance of an intact effector immune system to suppress CMV reactivation in normal individuals, we studied the impact of immunosuppression on the frequencies, function and phenotype of CMV-specific CD8+ T cells in a cohort of LTR. Methods: LTR, with known donor/recipient (D/R) CMV serostatus, were cross-sectionally studied before and following (1, 2, and 3 months post) lung transplantation. The frequency and functional characteristics of circulating CMV-specific CD8+ T lymphocytes was assessed by binding of specific tetrameric peptide/HLA complexes and peptide-induced interferon-γ (IFN-γ) production, respectively. HLA-A2, -B7, and –B8 CMV-specific epitopes were used as CD8+ antigenic stimulants. Phenotypic classification of CD8+ T cells into naïve, memory and effector subsets was based on the expression of the four T cell surface markers, CD27, CD28, CD45RA and CCR7. CMV viral load measurements were made in the plasma and bronchoalveolar lavage (BAL) using the COBAS Amplicor CMV monitor test. Results: The frequencies of CMV-specific CD8+ T cells varied considerably between CMV-seropositive LTR (range 0.1-8.1% of all CD8+ T cells), but remained relatively stable over time in any one individual, and were not significantly reduced compared to pre-transplant levels. In those “at-risk” LTR (CMV serostatus D+/R+, D+/R- and D-/R+) who did not demonstrate CMV reactivation during the study period, there was no evidence of any functional impairment in their CMV-specific CD8+ T cell subset (50-70% of tetramer positive CD8+ T cells produced IFN-γ following specific CMV peptide stimulation). In those LTR who were mismatched for CMV (D+/R-) the appearance of CMV-specific immunity (circulating tetramer positive CD8+ T cells) was often not associated with either a clinical CMV syndrome or measurable CMV DNA (viral load <400 copies) in the blood or BAL. Following primary CMV infection, CMV-specific CD8+ T cells were skewed predominantly towards an effector phenotype, CD45RA+/−CCR7- or CD27+/−CD28-. Conclusions: The maintenance of CMV latency in immunosuppressed CMV seropositive lung transplant recipients is associated with the persistence of functionally active circulating CMV-specific CD8+ T cells. Combining the measurement of CMV viral load with a detailed analysis of the frequency, function and phenotype of CMV-specific CD8+ T lymphocytes offers insights into the dynamic relationship that exists between host immunity and viral replication, particularly in the transplant setting.

Cytomegalovirus reactivation following allogeneic stem cell transplantation is associated with the presence of dysfunctional antigen-specific CD8+ T cells

Cytomegalovirus (CMV) infection causes significant morbidity and mortality in the setting of immunodeficiency, including the immune reconstitution phase following allogeneic stem cell transplantation (SCT). We assessed CMV-specific CD4(+) and CD8(+) T-cell responses in 87 HLA-A*0201-positive (A2+) and/or B*0702-positive (B7+) allogeneic stem cell transplant recipients using HLA-peptide tetramer staining and cytokine flow cytometry (CFC) to examine the association of CMV-specific immune reconstitution and CMV antigenemia following SCT. Strong CMV-specific T-cell responses recovered in most subjects (77 of 87, 88%) after SCT. Frequencies of CMV-specific CD8(+) T cells were significantly higher in those subjects who experienced early antigenemia relative to those who did not (2.2% vs 0.33%, P =.0002), as were frequencies of CMV-specific CD4(+) T cells (1.71% vs 0.75%, P =.002). Frequencies of CMV-specific CD8(+) T cells were also higher in subjects experiencing late antigenemia (2.4% vs 0.57%). When we combined tetramer staining and an assessment of cytokine production in a single assay, we found that individuals who experienced CMV antigenemia had lower tumor necrosis factor-alpha (TNF-alpha)-producing fractions of tetramer-staining CMV-specific CD8(+) T cells than subjects who did not (25% vs 65%, P =.015). Furthermore, individuals at high risk for CMV reactivation, including patients with acute graft-versus-host disease and those receiving steroids, had low fractions of cytokine-producing CMV-specific CD8(+) T cells (25% and 27%, respectively). These data suggest that the inability to control CMV reactivation following allogeneic SCT is due to the impaired function of antigen-specific CD8(+) T cells rather than an inability to recover sufficient numbers of CMV-specific T cells.

Purification of cytomegalovirus‐specific CD8 T cells from peripheral blood using HLA–peptide tetramers

Cytomegalovirus (CMV) reactivation and disease remains an important clinical problem for patients after allogeneic stem cell transplantation. Impaired cellular immune control of viral replication is responsible for viral reactivation, and transfer of CMV-specific T cells from transplant donors can be effective in providing protection. Recent reports have indicated that the frequency of CMV-specific CD8(+) T cells in the peripheral blood of healthy donors is surprisingly high. Here we demonstrate that by using a combination of human leucocyte antigen (HLA) Class I-peptide tetramers and magnetic selection it is possible to select CMV-specific T cells from CMV antibody-positive individuals to high purity. Reliable purification of CMV-specific T cells up to 99.8% of CD8(+) cells was possible within hours, even when starting with a precursor frequency of < 0.1% of peripheral blood CD8(+) T cells. CMV-specific T cells remained functional after the selection process. This novel form of antigen-specific T-cell selection should facilitate the selection of T cells for cellular immunotherapy to treat or prevent CMV disease after transplantation. In addition, this technique could potentially be applied to many antigens including against other infective agents and tumour-specific antigens.

Differentiation of cytomegalovirus-specific CD8+ T cells in healthy and immunosuppressed virus carriers

AbstractDuring immunosuppression, cytomegalovirus (CMV) can reactivate and cause serious clinical problems. Normally, abundant virus replication is suppressed by immune effector mechanisms. To study the interaction between CD8+ T cells and persisting viruses, frequencies and phenotypes of CMV-specific CD8+ T cells were determined in healthy individuals and compared to those in renal transplant recipients. In healthy donors, function of circulating virus-specific CD8+ T cells, as measured by peptide-induced interferon γ (IFN-γ) production, but not the number of virus-specific T cells enumerated by binding of specific tetrameric peptide/HLA complexes, correlated with the number of CMV-specific IFN-γ–secreting CD4+ helper T cells. Circulating CMV- specific CD8+ T cells did not express CCR7 and may therefore not be able to recirculate through peripheral lymph nodes. Based on coexpression of CD27 and CD45R0 most CMV-specific T cells in healthy donors appeared to be memory-type cells. Remarkably, frequencies of CMV-specific CD8+ T cells were significantly higher in immunosuppressed individuals than in healthy donors. In these patients CMV-specific cells predominantly had an effector phenotype, that is, CD45R0+CD27−CCR7− or CD45RA+CD27−CCR7− and contained both granzyme B and perforin. Our data show that in response to immunosuppressive medication quantitative and qualitative changes occur in the CD8+ T-cell compartment. These adaptations may be instrumental to maintain CMV latency.