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We investigated immune responses against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) among a group of convalescent, potential blood donors in Germany who had PCR-confirmed SARS-CoV-2 infection. Sixty days after onset of symptoms, 13/78 (17%) study participants had borderline or negative results to an ELISA detecting IgG against the S1 protein of SARS-CoV-2. We analyzed participants with PCR-confirmed infection who had strong antibody responses (ratio >3) as positive controls and participants without symptoms of SARS-CoV-2 infection and without household contact with infected patients as negative controls. Using interferon-γ ELISpot, we observed that 78% of PCR-positive volunteers with undetectable antibodies showed T cell immunity against SARS-CoV-2. We observed a similar frequency (80%) of T-cell immunity in convalescent donors with strong antibody responses but did not detect immunity in negative controls. We concluded that, in convalescent patients with undetectable SARS-CoV-2 IgG, immunity may be mediated through T cells.

The effects of mesenchymal stem cell (MSC)‐derived extracellular vesicles were compared with those of MSCs i.v. delivered 1, 3, and 5 days or 1 day after focal cerebral ischemia in mice. Motor coordination deficits, brain injury, immune responses in peripheral blood and brain, and cerebral angiogenesis and neurogenesis were analyzed. Postischemic immunosuppression was attenuated in peripheral blood 6 days after ischemia, providing an appropriate external milieu for successful brain remodeling. Although the initial concepts of stem cell therapy aimed at replacing lost tissue, more recent evidence has suggested that stem and progenitor cells alike promote postischemic neurological recovery by secreted factors that restore the injured brain's capacity to reshape. Specifically, extracellular vesicles (EVs) derived from stem cells such as exosomes have recently been suggested to mediate restorative stem cell effects. In order to define whether EVs indeed improve postischemic neurological impairment and brain remodeling, we systematically compared the effects of mesenchymal stem cell (MSC)‐derived EVs (MSC‐EVs) with MSCs that were i.v. delivered to mice on days 1, 3, and 5 (MSC‐EVs) or on day 1 (MSCs) after focal cerebral ischemia in C57BL6 mice. For as long as 28 days after stroke, motor coordination deficits, histological brain injury, immune responses in the peripheral blood and brain, and cerebral angiogenesis and neurogenesis were analyzed. Improved neurological impairment and long‐term neuroprotection associated with enhanced angioneurogenesis were noticed in stroke mice receiving EVs from two different bone marrow‐derived MSC lineages. MSC‐EV administration closely resembled responses to MSCs and persisted throughout the observation period. Although cerebral immune cell infiltration was not affected by MSC‐EVs, postischemic immunosuppression (i.e., B‐cell, natural killer cell, and T‐cell lymphopenia) was attenuated in the peripheral blood at 6 days after ischemia, providing an appropriate external milieu for successful brain remodeling. Because MSC‐EVs have recently been shown to be apparently safe in humans, the present study provides clinically relevant evidence warranting rapid proof‐of‐concept studies in stroke patients. Significance Transplantation of mesenchymal stem cells (MSCs) offers an interesting adjuvant approach next to thrombolysis for treatment of ischemic stroke. However, MSCs are not integrated into residing neural networks but act indirectly, inducing neuroprotection and promoting neuroregeneration. Although the mechanisms by which MSCs act are still elusive, recent evidence has suggested that extracellular vesicles (EVs) might be responsible for MSC‐induced effects under physiological and pathological conditions. The present study has demonstrated that EVs are not inferior to MSCs in a rodent stroke model. EVs induce long‐term neuroprotection, promote neuroregeneration and neurological recovery, and modulate peripheral post‐stroke immune responses. Also, because EVs are well‐tolerated in humans, as previously reported, the administration of EVs under clinical settings might set the path for a novel and innovative therapeutic stroke concept without the putative side effects attached to stem cell transplantation.

Cellular immunotherapy using chimeric antigen receptors (CARs) so far has almost exclusively used autologous peripheral blood-derived T cells as immune effector cells. However, harvesting sufficient numbers of T cells is often challenging in heavily pre-treated patients with malignancies and perturbed hematopoiesis and perturbed hematopoiesis. Also, such a CAR product will always be specific for the individual patient. In contrast, NK cell infusions can be performed in non-HLA-matched settings due to the absence of alloreactivity of these innate immune cells. Still, the infused NK cells are subject to recognition and rejection by the patient’s immune system, thereby limiting their life-span in vivo and undermining the possibility for multiple infusions. Here, we designed genome editing and advanced lentiviral transduction protocols to render primary human NK cells unsusceptible/resistant to an allogeneic response by the recipient’s CD8 + T cells. After knocking-out surface expression of HLA class I molecules by targeting the B2M gene via CRISPR/Cas9, we also co-expressed a single-chain HLA-E molecule, thereby preventing NK cell fratricide of B2M-knockout (KO) cells via “missing self”-induced lysis. Importantly, these genetically engineered NK cells were functionally indistinguishable from their unmodified counterparts with regard to their phenotype and their natural cytotoxicity towards different AML cell lines. In co-culture assays, B2M-KO NK cells neither induced immune responses of allogeneic T cells nor re-activated allogeneic T cells which had been expanded/primed using irradiated PBMNCs of the respective NK cell donor. Our study demonstrates the feasibility of genome editing in primary allogeneic NK cells to diminish their recognition and killing by mismatched T cells and is an important prerequisite for using non-HLA-matched primary human NK cells as readily available, “off-the-shelf” immune effectors for a variety of immunotherapy indications in human cancer.

Automated medical image analysis systems often require large amounts of training data with high quality labels, which are difficult and time consuming to generate. This paper introduces Radiology Object in COntext version 2 (ROCOv2), a multimodal dataset consisting of radiological images and associated medical concepts and captions extracted from the PMC Open Access subset. It is an updated version of the ROCO dataset published in 2018, and adds 35,705 new images added to PMC since 2018. It further provides manually curated concepts for imaging modalities with additional anatomical and directional concepts for X-rays. The dataset consists of 79,789 images and has been used, with minor modifications, in the concept detection and caption prediction tasks of ImageCLEFmedical Caption 2023. The dataset is suitable for training image annotation models based on image-caption pairs, or for multi-label image classification using Unified Medical Language System (UMLS) concepts provided with each image. In addition, it can serve for pre-training of medical domain models, and evaluation of deep learning models for multi-task learning.

Hematopoietic stem cell transplant (HSCT) recipients have a high risk of developing primary varicella-zoster virus (VZV) infection and reactivation. VZV vaccination may prevent infection and reactivation. In the current study, recipients of allogeneic HSCT (34 females, 45 males) were vaccinated with adjuvanted, recombinant zoster vaccine Shingrix™, which contains the VZV glycoprotein E. Cellular immunity against various VZV antigens was analyzed by interferon-gamma ELISpot. Peripheral blood mononuclear cells (PBMC) of recipients with versus without prior shingles (n = 36 and n = 43, respectively) showed approximately twofold higher VZV-specific responses prior to and post vaccination. After the first and second vaccination, ELISpot responses towards the glycoprotein E were significantly higher in males versus females (median of spots increment 18 versus 1 and 17 versus 4, respectively, p ≤ 0.02 each). Multivariate analysis showed that shingles and sex both impacts significantly on VZV immunity. Whereas vaccination-induced changes could hardly be detected after stimulation with a whole VZV antigen, there was a significant increase in responses towards glycoprotein E after vaccination (p < 0.005). These data indicate that vaccination with Shingrix™ augmented cellular, VZV-specific immunity in HSCT recipients. Shingles and male sex could both be identified as factors leading to increased immunity.

Extracellular vesicles (EVs) provide a complex means of intercellular signalling between cells at local and distant sites, both within and between different organs. According to their cell-type specific signatures, EVs can function as a novel class of biomarkers for a variety of diseases, and can be used as drug-delivery vehicles. Furthermore, EVs from certain cell types exert beneficial effects in regenerative medicine and for immune modulation. Several techniques are available to harvest EVs from various body fluids or cell culture supernatants. Classically, differential centrifugation, density gradient centrifugation, size-exclusion chromatography and immunocapturing-based methods are used to harvest EVs from EV-containing liquids. Owing to limitations in the scalability of any of these methods, we designed and optimised a polyethylene glycol (PEG)-based precipitation method to enrich EVs from cell culture supernatants. We demonstrate the reproducibility and scalability of this method and compared its efficacy with more classical EV-harvesting methods. We show that washing of the PEG pellet and the re-precipitation by ultracentrifugation remove a huge proportion of PEG co-precipitated molecules such as bovine serum albumine (BSA). However, supported by the results of the size exclusion chromatography, which revealed a higher purity in terms of particles per milligram protein of the obtained EV samples, PEG-prepared EV samples most likely still contain a certain percentage of other non-EV associated molecules. Since PEG-enriched EVs revealed the same therapeutic activity in an ischemic stroke model than corresponding cells, it is unlikely that such co-purified molecules negatively affect the functional properties of obtained EV samples. In summary, maybe not being the purification method of choice if molecular profiling of pure EV samples is intended, the optimised PEG protocol is a scalable and reproducible method, which can easily be adopted by laboratories equipped with an ultracentrifuge to enrich for functional active EVs.

Human mesenchymal stromal cell (MSC)-derived extracellular vesicles (EV) revealed neuroprotective potentials in various brain injury models, including neonatal encephalopathy caused by hypoxia-ischemia (HI). However, for clinical translation of an MSC-EV therapy, scaled manufacturing strategies are required, which is challenging with primary MSCs due to inter- and intra-donor heterogeneities. Therefore, we established a clonally expanded and immortalized human MSC line (ciMSC) and compared the neuroprotective potential of their EVs with EVs from primary MSCs in a murine model of HI-induced brain injury. In vivo activities of ciMSC-EVs were comprehensively characterized according to their proposed multimodal mechanisms of action. Nine-day-old C57BL/6 mice were exposed to HI followed by repetitive intranasal delivery of primary MSC-EVs or ciMSC-EVs 1, 3, and 5 days after HI. Sham-operated animals served as healthy controls. To compare neuroprotective effects of both EV preparations, total and regional brain atrophy was assessed by cresyl-violet-staining 7 days after HI. Immunohistochemistry, western blot, and real-time PCR were performed to investigate neuroinflammatory and regenerative processes. The amount of peripheral inflammatory mediators was evaluated by multiplex analyses in serum samples. Intranasal delivery of ciMSC-EVs and primary MSC-EVs comparably protected neonatal mice from HI-induced brain tissue atrophy. Mechanistically, ciMSC-EV application reduced microglia activation and astrogliosis, endothelial activation, and leukocyte infiltration. These effects were associated with a downregulation of the pro-inflammatory cytokine IL-1 beta and an elevated expression of the anti-inflammatory cytokines IL-4 and TGF-beta in the brain, while concentrations of cytokines in the peripheral blood were not affected. ciMSC-EV-mediated anti-inflammatory effects in the brain were accompanied by an increased neural progenitor and endothelial cell proliferation, oligodendrocyte maturation, and neurotrophic growth factor expression. Our data demonstrate that ciMSC-EVs conserve neuroprotective effects of primary MSC-EVs via inhibition of neuroinflammation and promotion of neuroregeneration. Since ciMSCs can overcome challenges associated with MSC heterogeneity, they appear as an ideal cell source for the scaled manufacturing of EV-based therapeutics to treat neonatal and possibly also adult brain injury.

The cellular response to SARS-CoV-2 vaccination and infection in allogeneic hematopoietic stem cell transplant (HSCT) recipients is not yet clear. In the current study, HSCT recipients prior to and post vaccination were tested for SARS-CoV-2-specific humoral and cellular immunity. Antibodies against spike (S) 1 were assessed by Anti-SARS-CoV-2 IgG ELISA (Euroimmun). Cellular immunity was analyzed by an in house interferon-gamma ELISpot and T-SPOT.COVID (Oxford Immunotec), using altogether seven SARS-CoV-2-specific antigens. In 117 HSCT patients vaccinated twice, SARS-CoV-2 IgG antibodies were significantly higher than in HSCT controls pre vaccination (p < 0.0001). After the second vaccination, we observed a median antibody ratio of 4.7 and 68% positive results, whereas 35 healthy controls reached a median ratio of 9.0 and 100% positivity. ELISpot responses in patients were significantly (p < 0.001) reduced to ≤33% of the controls. After the second vaccination, female HSCT patients and female healthy controls showed significantly higher antibody responses than males (6.0 vs. 2.1 and 9.2 vs. 8.2, respectively; p < 0.05). Cellular immunity was diminished in patients irrespective of sex. In conclusion, especially male HSCT recipients showed impaired antibody responses after SARS-CoV-2 vaccination. Changing the vaccine schedule or composition could help increase vaccine responses.

Tumor immune escape is associated with both, the expression of immune checkpoint molecules on peripheral immune cells and soluble forms of the human leukocyte antigen-G (HLA-G) in the blood, which are consequently discussed as clinical biomarker for disease status and outcome of cancer patients. HLA-G preferentially interacts with the inhibitory receptor immunoglobulin-like transcript (ILT) receptor-2 in the blood and can be secreted as free soluble molecules (sHLA-G) or via extracellular vesicles (EV). To investigate the contribution of these two forms to the expression of checkpoint molecules in peripheral blood, we primed peripheral blood mononuclear cells with purified soluble sHLA-G1 protein, or EV preparations derived from SUM149 cells transfected with membrane-bound HLA-G1 or control vector prior to anti-CD3/CD28 T cell activation. Our study demonstrated that priming of PBMC with sHLA-G1 protein prior to 48 h activation resulted in enhanced frequencies of ILT-2 expressing CD8 T cells, and in an upregulation of immune checkpoint molecules CTLA-4, PD-1, TIM-3, and CD95 exclusively on ILT-2 positive CD8 T cells. In contrast, when PBMC were primed with EV (containing HLA-G1 or not) upregulation of CTLA-4, PD-1, TIM-3, and CD95 occurred exclusively on ILT-2 negative CD8 T cells. Taken together, our data suggest that priming with sHLA-G forms induces a pronounced immunosuppressive/exhausted phenotype and that priming with sHLA-G1 protein or EV derived from HLA-G1 positive or negative SUM149 cells affects CD8 T cells complementary by targeting either the ILT-2 positive or negative subpopulation, respectively, after T cell activation.

HLA-G is a nonclassical HLA class I molecule. In allogeneic situations such as pregnancy or allograft transplantation, the expression of HLA-G has been related to a better acceptance of the fetus or the allograft. Thus, it seems that HLA-G is crucially involved in mechanisms shaping an allogeneic immune response into tolerance. In this contribution we focus on (i) how HLA-G is involved in transplantation and human reproduction, (ii) how HLA-G is regulated by genetic and microenvironmental factors, and (iii) how HLA-G can offer novel perspectives with respect to therapy.