Since being identified in China in December 2019, coronavirus disease 2019 has rapidly evolved into a global pandemic with over 4 million cases and more than 270,000 deaths.(1) Following the first reported cases in the United Kingdom (UK) in late January 2020, numbers have continued to rise with 223,060 cases and 32,065 deaths reported as of 11 th May 2020.(2) Initial reports from China have indicated that Covid-19 has an overall mortality rate of 1.4%. However, the prognosis varies widely between groups, with age over 60 years and underlying conditions including hypertension, diabetes, cardiovascular disease and cancer identified as risk factors for severe disease and death.(3) The initial reports from China show that patients with cancer are over-represented among individuals who develop severe Covid-19 after contracting the virus.(4) Patients with haematological malignancies are expected to be at increased risk of adverse outcomes from this viral infection, due being immunosuppressed as a consequence of the underlying cancer, and from the effects of therapy. This has led to a variety of recommendations to reduce the risk from Covid-19, including "shielding" by self-isolating at home for prolonged periods, and alterations to therapy such as delaying or even omitting chemotherapy, radiotherapy or transplantation.(5-8) However, at the time of writing there is virtually no published data on the impact of Covid-19 in patients with haematological malignancies.

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Classical Hodgkin Lymphoma (CHL) is unusually sensitive to PD1 inhibition and PDL1 is highly expressed on CHL cells and in the tumor microenvironment. This could be interpreted as evidence of exhaustion, but paradoxically, PD1+ lymphocyte infiltration does not predict PD1 inhibitor response and no increase in cytotoxic markers is seen after PD1 therapy as might be expected with reversal of exhaustion. In contrast to PD1, elevated PDL1 does predict response to PD1 inhibitors and recent data associate both retained CHL MHC-II expression and increased T helper (TH) T-cell receptor diversity with response suggesting a connection to the TH compartment. We performed a phenotypic, spatial and functional assessment of T cell exhaustion in CHL and found lower PD1 expression and exhaustion marker co-expression in CHL as compared to reactive nodes and similar proliferative and cytokine production capacity. We found no correlation between PDL1 expression and exhaustion signatures. Instead, we identified a strong association between PDL1 expression and CHL MHC-II expression, TH recruitment, and enrichment of Th1 regulatory cells. These data suggest that a dominant effect of PDL1 expression in CHL may be T helper engagement and promotion of regulatory microenvironment rather than maintenance of exhaustion.

Platelets are an essential component of the first step in the process of haemostasis, plugging defects in the endothelium and providing a surface for secondary haemostasis to occur, via the coagulation pathway. Platelet aggregation and activation cause granule release of von Willebrand factor, ADP and serotonin, which, in turn, results in recruitment of more platelets to form the platelet plug. This serves to stop the bleeding, and also to activate the coagulation pathway on the surface of the activated platelets, leading to a firm fibrin clot.