Lowest numbers of primary CD8(+) T cells can reconstitute protective immunity upon adoptive immunotherapy.

Patients undergoing allogeneic hematopoietic stem cell transplantation (allo-HSCT) are threatened by potentially lethal viral manifestations like cytomegalovirus (CMV) reactivation. Because the success of today's virostatic treatment is limited by side effects and resistance development, adoptive transfer of virus-specific memory T cells derived from the stem cell donor has been proposed as an alternative therapeutic strategy. In this context, dose minimization of adoptively transferred T cells might be warranted for the avoidance of graft-versus-host disease (GVHD), in particular in prophylactic settings after T-cell-depleting allo-HSCT protocols. To establish a lower limit for successful adoptive T-cell therapy, we conducted low-dose CD8(+) T-cell transfers in the well-established murine Listeria monocytogenes (L.m.) infection model. Major histocompatibility complex-Streptamer-enriched antigen-specific CD62L(hi) but not CD62L(lo) CD8(+) memory T cells proliferated, differentiated, and protected against L.m. infections after prophylactic application. Even progenies derived from a single CD62L(hi) L.m.-specific CD8(+) T cell could be protective against bacterial challenge. In analogy, low-dose transfers of Streptamer-enriched human CMV-specific CD8(+) T cells into allo-HSCT recipients led to strong pathogen-specific T-cell expansion in a compassionate-use setting. In summary, low-dose adoptive T-cell transfer (ACT) could be a promising strategy, particularly for prophylactic treatment of infectious complications after allo-HSCT.

Targeted delivery of CD40L promotes restricted activation of antigen-presenting cells and induction of cancer cell death.

BACKGROUND: Stimulation of CD40 can augment anti-cancer T cell immune responses by triggering effective activation and maturation of antigen-presenting cells (APCs). Although CD40 agonists have clinical activity in humans, the associated systemic activation of the immune system triggers dose-limiting side-effects. METHODS: To increase the tumor selectivity of CD40 agonist-based therapies, we developed an approach in which soluble trimeric CD40L (sCD40L) is genetically fused to tumor targeting antibody fragments, yielding scFv:CD40L fusion proteins. We hypothesized that scFv:CD40L fusion proteins would have reduced CD40 agonist activity similar to sCD40L but will be converted to a highly agonistic membrane CD40L-like form of CD40L upon anchoring to cell surface exposed antigen via the scFv domain. RESULTS: Targeted delivery of CD40L to the carcinoma marker EpCAM on carcinoma cells induced dose-dependent paracrine maturation of DCs ~20-fold more effective than a non-targeted control scFv:CD40L fusion protein. Similarly, targeted delivery of CD40L to the B cell leukemia marker CD20 induced effective paracrine maturation of DCs. Of note, the CD20-selective delivery of CD40L also triggered loss of cell viability in certain B cell leukemic cell lines as a result of CD20-induced apoptosis. CONCLUSIONS: Targeted delivery of CD40L to cancer cells is a promising strategy that may help to trigger cancer-localized activation of CD40 and can be modified to exert additional anti-cancer activity via the targeting domain.

T-cell therapy for cytomegalovirus infection.

PURPOSE OF REVIEW: Human cytomegalovirus (CMV) reactivation and disease remains one of the major complications after allogeneic haemopoietic stem cell transplantation. Cell-mediated immunity is essential in counteracting CMV infection as evident by detection of high frequencies of CMV-specific CD8 and CD4 lymphocytes among the healthy CMV-seropositive individuals. Adoptive transfer of CMV-specific T cells to speed up reconstitution of CMV-specific immunity potentially offers clinical protection and reduces drug toxicities as well as outgrowth of drug-resistant strains from prolonged antiviral therapy. RECENT FINDINGS: Different strategies to generate CMV-specific T cell have been explored. Similarly, vast diversities in term of cell dose and composition of the cellular product have been infused into small cohorts of patients. To date, a number of phase I/II clinical trials have demonstrated the feasibility of adoptive transferred CMV-specific T cells as prophylaxis, pre-emptive or therapeutic measure. In general, all these strategies showed variable degrees of efficacy without obvious adverse event particularly with regard to the induction of graft-versus-host disease. SUMMARY: In this review, we would like to give a comprehensive synopsis regarding therapeutic application of CMV-specific T cells in fighting CMV infection.

Targeted in-vitro-stimulation reveals highly proliferative multi-virus-specific human central memory T cells as candidates for prophylactic T cell therapy.

Adoptive T cell therapy (ACT) has become a treatment option for viral reactivations in patients undergoing allogeneic hematopoietic stem cell transplantation (alloHSCT). Animal models have shown that pathogen-specific central memory T cells (TCM) are protective even at low numbers and show long-term survival, extensive proliferation and high plasticity after adoptive transfer. Concomitantly, our own recent clinical data demonstrate that minimal doses of purified (not in-vitro- expanded) human CMV epitope-specific T cells can be sufficient to clear viremia. However, it remains to be determined if human virus-specific TCM show the same promising features for ACT as their murine counterparts. Using a peptide specific proliferation assay (PSPA) we studied the human Adenovirus- (AdV), Cytomegalovirus- (CMV) and Epstein-Barr virus- (EBV) specific TCM repertoires and determined their functional and proliferative capacities in vitro. TCM products were generated from buffy coats, as well as from non-mobilized and mobilized apheresis products either by flow cytometry-based cell sorting or magnetic cell enrichment using reversible Fab-Streptamers. Adjusted to virus serology and human leukocyte antigen (HLA)-typing, donor samples were analyzed with MHC multimer- and intracellular cytokine staining (ICS) before and after PSPA. TCM cultures showed strong proliferation of a plethora of functional virus-specific T cells. Using PSPA, we could unveil tiniest virus epitope-specific TCM populations, which had remained undetectable in conventional ex-vivo-staining. Furthermore, we could confirm these characteristics for mobilized apheresis- and GMP-grade Fab-Streptamer-purified TCM products. Consequently, we conclude that TCM bare high potential for prophylactic low-dose ACT. In addition, use of Fab-Streptamer-purified TCM allows circumventing regulatory restrictions typically found in conventional ACT product generation. These GMP-compatible TCM can now be used as a broad-spectrum antiviral T cell prophylaxis in alloHSCT patients and PSPA is going to be an indispensable tool for advanced TCM characterization during concomitant immune monitoring.

Heterogeneity of Specific CD4+ and CD8+ T Cells Stimulated by CMV pp65 and IE1 Antigens.

Characterization of human cytomegalovirus-specific T cells (CMV-T) is of critical importance for their potential use in adoptive immunotherapy after allogeneic hematopoietic stem cell transplantation. Background frequencies of CMV-T in peripheral blood mononuclear cells (PBMCs) of CMV-seropositive healthy subjects are usually very low, hence the requirement for prolonged culture time and multiple stimulations to expand them. The evaluation of the end-culture specificity and composition has sometimes been neglected or difficult to assess in these settings. We explored the identity and the functionality of pp65-specific and IE1-specific T cells, enriched in short-term cultures from PBMCs. Antigen-specific T cells were further isolated by IFN-γ capture system and/or CD154 microbeads. Frequency of IE1-specific cytotoxic T cells in PBMCs secreting IFN-γ was higher compared with the pp65-specific one, whereas the latter cell types showed a higher median CD107a degranulation. Cell viability, rate of CMV-T increase, and multicytokine secretion profile after epitope-specific short-term cultures were heterogenous. T cells were mainly of late effector stages but they significantly dropped off upon CMV rechallenge with peptide pools. In parallel, CMV-T expansion was accompanied by a significant increase of cytotoxic naive/memory stem cells (CTLs), whereas the CD4 counterpart significantly increased only upon stimulation with IE1. Outcome was variable and showed donor and epitope dependency. Differences in human leukocyte antigen and epitope dominance and variability in the relative number of CD3 effector cells and IFN-γ/CD154 expression among healthy donors could reflect the observed individual CMV-specific cellular immunity. This heterogeneity raises points to be considered when approaching adoptive immunotherapy.

Correlation Between Tear Film Osmolarity and the Disease Score of the International Chronic Ocular Graft-Versus-Host-Disease Consensus Group in Hematopoietic Stem Cell Transplantation Patients.

PURPOSE: To evaluate tear film osmolarity (TFO) as a diagnostic tool for detecting chronic ocular graft-versus-host disease (GVHD) in patients after hematopoietic stem cell transplantation and to assess its correlation with the new international chronic ocular GVHD score. METHODS: A group of 204 consecutive patients who underwent hematopoietic stem cell transplantation at University Hospital Wuerzburg in Germany received an ophthalmologic examination after transplantation. TFO was measured and the chronic ocular GVHD score was calculated based on the Schirmer test, corneal fluorescein staining, conjunctival injection, Ocular Surface Disease Index questionnaire, and presence of systemic GVHD. RESULTS: A total of 172 patients showed no chronic ocular GVHD. Of the remaining 32 patients using the international chronic ocular GVHD score, 21 were classified as "probably" and 11 as "definite" chronic ocular GVHD. TFO was positively correlated with the new chronic ocular GVHD score (P < 0.01, r = 0.35). TFO differed significantly between patients with no ocular GVHD (300 ± 16.5 mOsm/L) and definite ocular GVHD (337 ± 36 mOsm/L)-a receiver operating characteristic analysis showed high discrimination capability (area under the curve: 0.91 ± 0.04) and suggested a threshold level of the TFO value of 312 mOsm/L yielding a sensitivity of 91% and a specificity of 82%. CONCLUSIONS: TFO can be used for detecting chronic ocular GVHD with high sensitivity and specificity as a noninvasive objective test in addition to traditional dry eye tests. It correlates positively with the diagnostic criteria of a recently established international consensus score for diagnosing the disease.