Host immune response in immunodeficient mice against infection with Cryptosporidium parvum

Immunantwort von immundefizienten Mäusen gegenüber Infektionen mit Cryptosporidium parvum. Cryptosporidium parvum ist ein intrazellulärer, protozoischer Krankheitserreger, der im immunkompromittierten Wirt zu lebensbedrohender Enteritis führen kann. CD4+ T-Zellen und Interferon (IFN)-γ spielen wesentliche Rollen bei der Wirtsimmunantwort gegen die Infektion. Dennoch sind die Effektormechanismen, die zur Resistenz führen nur wenig verstanden. In dieser Studie wurde die Immunantwort von IFN-γ- und Interleukin (IL)-12-Defektmäusen parallel zu Wildtypmäusen analysiert. Die Ergebnisse identifizierten IFN-γ als Schlüsselzytokin bei der natürlichen und erworbenen Immunität während der Erst- und Folgeinfektion mit C. parvum. Tumornekrosefaktor (TNF)-α ist möglicherweise ein Induktor der frühen IFN-γ-Antwort in IL-12 Knockout-Mäusen. Weiterhin tragen offenbar sowohl Th1- als auch Th2-Zytokine zur Überwindung der Primärinfektion bei, die ersten mehr als die letztgenannten. Zytokingene waren am Ort der Infektion (Ileum) dramatisch verändert, nicht aber in den lokalen Lymphknoten und der Milz. Nach Folgeinfektion ergab sich in Abwesenheit von IFN-γ eine signifikante Erhöhung der Th2-Zytokine IL-5 and IL-13. Die Ergebnisse zeigten weiterhin, dass das Th1-Zytokin IL-18 zur Resistenz gegenüber C. parvum beiträgt, möglicherweise durch verschiedene Immunfunktionen, wie der Regulation von Serum-IFN-γ während der Infektion und/oder der Erhaltung der Homeostase der Th1/Th2-Zytokine durch Regulation der Th2-Zytokine. Weiterhin zeigten diese Untersuchungen den Transfer von Resistenz gegenüber C. parvum von infizierten auf naïve Mäuse mittels stimulierter intraepithelialer Lymphozyten und CD4+ T-Zellen. Diese Ergebnisse weisen auf die Gegenwart von C. parvum-spezifischen CD4+ T-Zellen in anderen lymphatischen Geweben neben der Darmmukosa hin. Eine Stimulation der Spendertiere durch Infektion war notwendig für eine übertragbare schützende Immunität. Dennoch konnte die übertragene Immunität nicht die Infektion der Empfängertiere vollständig verhindern; eine Verdopplung der Spenderzellen führte zu keinem besseren Ergebnis. Weiterhin ergab der Transfer von CD4+ und CD8+ T-Zellen (Pan-T-Zellen) keinen erhöhten Schutz der naiven Empfängertiere als der alleinige Transfer von CD4+ T-Zellen. Dies weist auf die fehlende Bedeutung der CD8+ T-Zellen beim Schutz vor C. parvum-Infektion hin.

HLA class II mismatch alleles as targets of the alloreactive CD4 T-cell response

In allogeneic hematopoietic stem cell transplantation (allo-HSCT), alloreactive T lymphocytes of donor origin mediate the beneficial graft-versus-leukemia effect but also induce graft-versus-host disease (GvHD). Since human leukocyte antigens (HLA) mismatch alleles represent major targets of alloreactive T lymphocytes, patient and donor are usually matched for the class I molecules A, B, C, and for the class II molecules DRB1 and DQB1, in order do reduce the risk of GvHD. The HLA-DPB1 locus, however, is still ignored in donor selection. Interestingly, clinical studies have demonstrated that disparities at HLA-DQB1 alleles as well as distinct HLA DPB1 mismatch constellations do not adversely affect the outcome of allo-HSCT. It has also been shown that HLA class II is predominantly expressed on hematopoietic cells under non-inflammatory conditions. Therefore, this PhD thesis focused on the application of CD4 T cells in adoptive immunotherapy of leukemias.rnIn the first part of this thesis we developed a rapid screening approach to detect T-cell reactivity of donors to single HLA class II mismatch alleles. Allo-HLA reactivity was measured in naive, memory, and entire CD4 T cells isolated from PBMC of healthy donors by flow cytometric cell sorting according to expression of the differentiation markers CD45RA, CD45RO, CD62L, and CCR7. T-cell populations were defined by a single marker to facilitate translation into a clinical-grade allo-depletion procedure. Alloreactivity to single HLA-DR/-DQ mismatch alleles was analyzed in short-term mixed lymphocyte reactions (MLR) in vitro. As standard antigen-presenting cells, we used the HLA-deficient cell line K562 upon electroporation with single HLA-DR/-DQ allele mRNA. We observed in IFN-γ ELISpot assays that allo-HLA-reactivity preferentially derived from subsets enriched for naive compared to memory T cells in healthy donors, irrespective of the HLA mismatch allele. This separation was most efficient if CD62L (P=0.008) or CD45RA (P=0.011) were used as marker. Median numbers of allo-HLA-reactive effector cells were 3.5-fold and 16.6-fold lower in CD62Lneg and CD45RAneg memory CD4 T cells than in entire CD4 T cells, respectively. In allele-specific analysis, alloreactivity to single HLA-DR alleles clearly exceeded that to HLA-DQ alleles. In terms of alloproliferation no significant difference could be observed between individual CD4 T-cell subsets. rnThe second part of this thesis dealed with the generation of allo-HLA-DQ/-DP specific CD4 T cells. Naive CD45RApos CD4 T cells isolated from healthy donor PBMC by flow cytometric cell sorting were stimulated in MLR against single allo-HLA-DQ/-DP alleles transfected into autologous mature monocyte-derived dendritic cells by mRNA electroporation. Rapidly expanding HLA-DQ/-DP mismatch reactive T cells significantly recognized and cytolysed primary acute myeloid leukemia (AML) blasts, fibroblasts (FB) and keratinocytes (KC) in IFN-γ ELISpot and 51chromium release assays if the targets carried the HLA DQ/ DP allele used for T cell priming. While AML blasts were recognized independent of pre-incubating them with IFN-γ, recognition of FB and KC required IFN-γ pre treatment. We further investigated HLA class II expression on hematopoietic and non-hematopoietic cells by flow cytometry. HLA class II was not detected on primary FB, KC, and non-malignant kidney cells, but was expressed at significant levels on primary AML blasts and B-LCL. Up-regulation of HLA class II expression was observed on all cell types after pre-incubation with IFN-γ.rnIn summary, the novel K562-HLA based MLR approach revealed that naive-depleted CD4 T-cell subsets of healthy individuals contain decreased allo-HLA reactivity in vitro. We propose the application of CD45RAneg naive-depleted CD4 T cells as memory T cell therapy, which might be beneficial for HLA-mismatched patients at high-risk of GvHD and low-risk of leukemia relapse. Memory T cells might also provide important post-transplant immune functions against infectious agents. Additionally, the screening approach could be employed as test system to detect donors which have low risks for the emergence of GvHD after allo-HSCT. In the second part of this thesis we developed a protocol for the generation of allo-HLA-DQ/-DP specific CD4 T cell lines, which could be applied in situations in which patient and donor are matched in all HLA alleles but one HLA-DQ/-DP allele with low GvHD potential. These T cells showed lytic activity to leukemia cells while presumably sparing non-hematopoietic tissues under non-inflammatory conditions. Therefore, they might be advantageous for allo-HSCT patients with advanced stage AML after reduced-intensity conditioning and T-cell depletion for the replenishment of anti-leukemic reactivity if the risk for disease relapse is high. rn