A T cell receptor targeting a recurrent driver mutation in FLT3 mediates elimination of primary human acute myeloid leukemia in vivo.

Acute myeloid leukemia (AML), the most frequent leukemia in adults, is driven by recurrent somatically acquired genetic lesions in a restricted number of genes. Treatment with tyrosine kinase inhibitors has demonstrated that targeting of prevalent FMS-related receptor tyrosine kinase 3 (FLT3) gain-of-function mutations can provide significant survival benefits for patients, although the efficacy of FLT3 inhibitors in eliminating FLT3-mutated clones is variable. We identified a T cell receptor (TCR) reactive to the recurrent D835Y driver mutation in the FLT3 tyrosine kinase domain (TCRFLT3D/Y). TCRFLT3D/Y-redirected T cells selectively eliminated primary human AML cells harboring the FLT3D835Y mutation in vitro and in vivo. TCRFLT3D/Y cells rejected both CD34+ and CD34- AML in mice engrafted with primary leukemia from patients, reaching minimal residual disease-negative levels, and eliminated primary CD34+ AML leukemia-propagating cells in vivo. Thus, T cells targeting a single shared mutation can provide efficient immunotherapy toward selective elimination of clonally involved primary AML cells in vivo.

Prevalent and immunodominant CD8 T cell epitopes are conserved in SARS-CoV-2 variants.

The emergence of SARS-CoV-2 variants of concern (VOC) is driven by mutations that mediate escape from neutralizing antibodies. There is also evidence that mutations can cause loss of T cell epitopes. However, studies on viral escape from T cell immunity have been hampered by uncertain estimates of epitope prevalence. Here, we map and quantify CD8 T cell responses to SARS-CoV-2-specific minimal epitopes in blood drawn from April to June 2020 from 83 COVID-19 convalescents. Among 37 HLA ligands eluted from five prevalent alleles and an additional 86 predicted binders, we identify 29 epitopes with an immunoprevalence ranging from 3% to 100% among individuals expressing the relevant HLA allele. Mutations in VOC are reported in 10.3% of the epitopes, while 20.6% of the non-immunogenic peptides are mutated in VOC. The nine most prevalent epitopes are conserved in VOC. Thus, comprehensive mapping of epitope prevalence does not provide evidence that mutations in VOC are driven by escape of T cell immunity.

Nickel acts as an adjuvant during cobalt sensitization.

Metal allergy is the most frequent form of contact allergy with nickel and cobalt being the main culprits. Typically, exposure comes from metal-alloys where nickel and cobalt co-exist. Importantly, very little is known about how co-exposure to nickel and cobalt affects the immune system. We investigated these effects by using a recently developed mouse model. Mice were epicutaneously sensitized with i) nickel alone, ii) nickel in the presence of cobalt, iii) cobalt alone, or iv) cobalt in the presence of nickel, and then followed by challenge with either nickel or cobalt alone. We found that sensitization with nickel alone induced more local inflammation than cobalt alone as measured by increased ear-swelling. Furthermore, the presence of nickel during sensitization to cobalt led to a stronger challenge response to cobalt as seen by increased ear-swelling and increased B and T cell responses in the draining lymph nodes compared to mice sensitized with cobalt alone. In contrast, the presence of cobalt during nickel sensitization only induced an increased CD8(+) T cell proliferation during challenge to nickel. Thus, the presence of nickel during cobalt sensitization potentiated the challenge response against cobalt more than the presence of cobalt during sensitization to nickel affected the challenge response against nickel. Taken together, our study demonstrates that sensitization with a mixture of nickel and cobalt leads to an increased immune response to both nickel and cobalt, especially to cobalt, and furthermore that the adjuvant effect appears to correlate with the inflammatory properties of the allergen.

An immune response study of oakmoss absolute and its constituents atranol and chloroatranol.

BACKGROUND: Atranol and chloroatranol are the main allergens of oakmoss absolute. However, the immune responses induced by these substances are poorly characterized. OBJECTIVES: To characterize immune responses induced by atranol, chloroatranol and oakmoss absolute in mice. METHODS: Mice were sensitized and challenged with various concentrations of atranol, chloroatranol, and oakmoss absolute. The immune responses were analysed as B cell infiltration, T cell proliferation in the draining lymph nodes, and expression of interleukin (IL)-18, IL-1ß and tumour necrosis factor-α in skin. The cytotoxicity of atranol and chloroatranol against keratinocytes was determined. RESULTS: Sensitization experiments showed that atranol, chloroatranol and oakmoss induced sensitization when applied in high concentrations. Challenge experiments showed that even low concentrations of atranol and chloroatranol induced sensitization. In parallel, atranol and chloroatranol elicited challenge reactions following sensitization with oakmoss. The magnitude of the immune response to the three allergens increased in the following order: atranol, chloroatranol, and oakmoss. The expression of proinflammatory cytokines was induced by chloroatranol and oakmoss, but not by atranol. Chloroatranol was found to be more cytotoxic than atranol against keratinocytes. CONCLUSIONS: Atranol and chloroatranol can elicit both sensitization and challenge reactions, but the mixture of allergens in oakmoss absolute is more potent than atranol and chloroatranol alone.

Enhanced sensitization and elicitation responses caused by mixtures of common fragrance allergens.

BACKGROUND: Perfumes are complex mixtures composed of many fragrance ingredients, many of which are known to be only weak allergens when tested individually. It is therefore surprising that fragrance contact allergy is one of the most common forms of contact allergy. OBJECTIVES: To investigate whether mixing different fragrance allergens leads to increased sensitization potency, and to examine the difference in the challenge response to one chemical in mice sensitized either with the mixture of allergens or with only the relevant allergen. METHODS: CBA mice were sensitized with three different concentrations of three fragrance allergens alone or as a mixture. The sensitization and elicitation responses were measured by ear thickness plus infiltration of B and T cells and T cell proliferation in the draining lymph nodes. RESULTS: We found a dose-dependent sensitization response for each of the allergens. An increased response was seen when the allergens were mixed. A stronger challenge response to cinnamal was seen in mice sensitized with the allergen mixture than in mice sensitized with cinnamal alone. CONCLUSIONS: Our findings suggest that mixtures of allergens increase the primary response that potentiates the generation of memory T cells in response to the specific allergen. Thus, allergen mixtures enhance both induction and elicitation of contact allergy.

Polymorphisms of the T cell receptor CD3delta and CD3epsilon chains affect anti-CD3 antibody binding and T cell activation.

T cell receptor (TCR) structure and function have been thoroughly studied for decades. Production and analyses of knock-out and knock-in mice with mutations in the CD3 chains have contributed significantly to these studies. The generation of such gene-modified mice relies on the availability of suitable embryonic stem (ES) cell lines. Traditionally, ES cell lines from the 129 mouse strains have been used followed by backcrossing to the C57BL/6 strain. In the present study, we demonstrate the existence of polymorphisms in the CD3 genes from mice of the 129 and C57BL/6 strains. These polymorphisms result in amino acid substitutions in the ectodomains of both the CD3delta and CD3epsilon chains in 129 mice compared to C57BL/6 mice. The amino acid substitutions do not change the stoichiometry or surface expression level of the TCR complex in 129 T cells but cause reduced anti-CD3 antibody binding to 129 T cells. Further, when stimulated with mitogenic anti-CD3 antibodies, T cells from the 129 strains show reduced expression of the activation marker CD69, Ca(2+) flux, IL-2 production and proliferative responses compared to C57BL/6 T cells. These findings demonstrate that polymorphisms of the CD3delta and epsilon ectodomains exist in mice, and that some of these polymorphisms lead to amino acid substitutions which cause structural changes and affect anti-CD3 antibody binding. Thus, functional T cell studies should be interpreted with caution when anti-CD3 antibodies are used for stimulation of T cells derived from gene-modified mice originating from 129 ES cell lines.

TCR down-regulation controls T cell homeostasis.

TCR and cytokine receptor signaling play key roles in the complex homeostatic mechanisms that maintain a relative stable number of T cells throughout life. Despite the homeostatic mechanisms, a slow decline in naive T cells is typically observed with age. The CD3gamma di-leucine-based motif controls TCR down-regulation and plays a central role in fine-tuning TCR expression and signaling in T cells. In this study, we show that the age-associated decline of naive T cells is strongly accelerated in CD3gammaLLAA knock-in mice homozygous for a double leucine to alanine mutation in the CD3gamma di-leucine-based motif, whereas the number of memory T cells is unaffected by the mutation. This results in premature T cell population senescence with a severe dominance of memory T cells and very few naive T cells in middle-aged to old CD3gamma mutant mice. The reduced number of naive T cells in CD3gamma mutant mice was caused by the combination of reduced thymic output, decreased T cell apoptosis, and increased transition of naive T cells to memory T cells. Experiments with bone marrow chimeric mice confirmed that the CD3gammaLLAA mutation exerted a T cell intrinsic effect on T cell homeostasis that resulted in an increased transition of CD3gammaLLAA naive T cells to memory T cells and a survival advantage of CD3gammaLLAA T cells compared with wild-type T cells. The experimental observations were further supported by mathematical modeling of T cell homeostasis. Our study thus identifies an important role of CD3gamma-mediated TCR down-regulation in T cell homeostasis.