Single dose of BNT162b2 mRNA vaccine against severe acute respiratory syndrome coronavirus‐2 (SARS‐CoV‐2) induces neutralising antibody and polyfunctional T‐cell responses in patients with chronic myeloid leukaemia

Summary Patients receiving targeted cancer treatments such as tyrosine kinase inhibitors (TKIs) have been classified in the clinically extremely vulnerable group to develop severe acute respiratory syndrome coronavirus‐2 (SARS‐CoV‐2), including patients with chronic myeloid leukaemia (CML) taking TKIs. In addition, concerns that immunocompromised individuals with solid and haematological malignancies may not mount an adequate immune response to a single dose of SARS‐CoV‐2 BNT162b2 (Pfizer‐BioNTech) vaccine have been raised. In the present study, we evaluated humoral and cellular immune responses after a first injection of BNT162b2 vaccine in 16 patients with CML. Seroconversion and cellular immune response before and after vaccination were assessed. By day 21 after vaccination, anti‐Spike immunoglobulin G was detected in 14/16 (87·5%) of the patients with CML and all developed a neutralising antibody response [serum dilution that inhibits 50% infection (ID50) >50], including medium (ID50 of 200–500) or high (ID50 of 501–2000) neutralising antibodies titres in nine of the 16 (56·25%) patients. T‐cell response was seen in 14/15 (93·3%) evaluable patients, with polyfunctional responses seen in 12/15 (80%) patients (polyfunctional CD4+ response nine of 15, polyfunctional CD8+ T‐cell response nine of 15). These data demonstrate the immunogenicity of a single dose of SARS‐CoV‐2 BNT162b2 vaccine in most patients with CML, with both neutralising antibodies and polyfunctional T‐cell responses seen in contrast to patients with solid tumour or lymphoid haematological malignancies.


Introduction
Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), a novel beta coronavirus, has led to unprecedented healthcare challenges on a global scale. Development of antiviral immunity is key to reducing spread of infection and gaining pandemic control. Impressive collaborative efforts have led to the rapid development of multiple efficacious vaccines against SARS-CoV-2. BNT162b2 is a nucleosidemodified mRNA that encodes a full-length Spike that is stabilised in the pre-fusion conformation of the SARS-CoV-2 Spike (S) protein, a key target of neutralising antibodies. However, concerns that immunocompromised individuals may not mount an adequate immune response after a single dose of vaccination have been raised, with early reports describing a reduced response in a heterogeneous group of patients with solid and haematological malignancies. 1 Patients with chronic myeloid leukaemia (CML) have been shown to have impaired innate and adaptive immunity, although most pronounced at diagnosis, leading to the decision of the Department of Health and Social Care (DHSC) to classify in the clinically extremely vulnerable groups 'people having other targeted cancer treatments that can affect the immune system, such as protein kinase inhibitors'. Immune response to vaccination may indeed be attenuated by tyrosine kinase inhibitors (TKIs), particularly those with greater 'off target' kinase inhibition, which we have previously shown to inhibit B-cell function and antibody response in vivo. 2 In the present study, we report an analysis of the Tcell and antibody responses following a single dose of BNT162b2 in patients with CML on TKI therapy.

Study design and vaccine
From 17 December 2020 until 17 February 2021, patients with a known diagnosis of myeloid haematological malignancies presenting at Guy's and St Thomas' NHS Foundation Trust and eligible to receive a 30 lg injection of SARS-CoV-2 mRNA BNT162b2 vaccine were approached for informed consent. Over that period, 16 adult patients with a diagnosis of chronic phase CML were vaccinated in compliance with UK DHSC guidelines and recruited. All patients gave informed consent and the study protocol was approved by the

Safety assessments
We solicited reports of local (pain, tenderness, redness, induration and ecchymosis) and systemic (fever, headache, malaise, myalgia, chills and nausea) adverse events by 2-weekly telephone calls performed by trained medical students and physician assistants. All local and systemic adverse events reported in response to solicitation within 7 days after administration of the vaccine were considered to be related to the vaccine.

Enzyme-linked immunosorbent assay (ELISA) protocol
The ELISAs were conducted as previously described. 3 All plasma samples were heat-inactivated at 56°C for 30 min before use. High-binding ELISA plates (Corning, 3690; Corning, NY, USA) were coated with antigen Nuclear (N) protein or the S glycoprotein at 3 µg/ml (25 µl/well) in phosphatebuffered saline (PBS), either overnight at 4°C or for 2 h at 37°C. Wells were washed with PBS-T (PBS with 0Á05% Tween-20) and then blocked with 100 µl of 5% milk in PBS-T for 1 h at room temperature. The wells were emptied and serial dilutions of plasma (starting at 1:25, sixfold dilution) were added and incubated for 2 h at room temperature. Control reagents included CR3009 (2 µg/ml; N-specific monoclonal antibody), CR3022 (0Á2 µg/ml; S-specific monoclonal antibody), negative control plasma (1:25 dilution), positive control plasma (1:50) and blank wells. Wells were washed with PBS-T. Secondary antibody was added and incubated for 1 h at room temperature. Immunoglobulin G (IgG) was detected using goat anti-human-Fc-alkaline phosphatase (AP; 1:1000; Jackson ImmunoResearch Europe Ltd, Ely, Cambridgeshire, UK; catalogue no. 109-055-098) and wells were washed with PBS-T and AP substrate (Sigma-Aldrich, St. Louis, MO, USA) was added and plates read at 405 nm. The half maximal effective concentration (EC 50 ) values were calculated in GraphPad Prism. Where an EC 50 was not reached at 1:25, plasma was considered seropositive if the optical density (OD) at 405 nm was fourfold above background and a value of 25 was assigned.

Neutralisation assay with SARS-CoV-2
Human immunodeficiency virus type-1 (HIV-1)-based virus particles, pseudotyped with SARS-CoV-2 Wuhan Spike were prepared in HEK-293T/17 cells and neutralisation assays were conducted as previously described. 3 Serial dilutions of plasma samples (heat inactivated at 56°C for 30 min) were prepared in Dulbecco's modified Eagle's medium (DMEM) complete media [10% fetal bovine serum, 1% penicillin/streptomycin (100 iu/ml penicillin and 100 mg/ml streptomycin)] and incubated with pseudotyped virus for 1 h at 37°C in 96-well plates. Next, HeLa cells stably expressing the angiotensinconverting enzyme 2 (ACE2) receptor (provided by Dr James Voss, Scripps Research, La Jolla, CA, USA) were added (12 500 cells/50 µl per well) and the plates were left for 72 h. Infection level was assessed in lysed cells with the Bright-Glo luciferase kit (Promega Corp., Madison, WI, USA), using a Victor TM X3 multi-label reader (PerkinElmer, Inc., Waltham, MA, USA). Measurements were performed in duplicate and the duplicates used to calculate the serum dilution that inhibits 50% infection (ID 50 ) using GraphPad Prism.

Patients' characteristics and toxicity profile of SARS-CoV-2 BNT162b2
Analysis was performed in the 16 patients with chronic phase CML, with clinical characteristics summarised in Table I. The vaccine was safe and tolerable in this patient group with localised inflammation reported in 56Á3% (nine) and a transient flu-like illness reported in 23Á5% (four) of patients (Table II). None of the 16 patients reported SARS-CoV-2 infection before enrolment or after inclusion in the study.

Seroconversion rates to BNT162b2 and neutralising antibody titres after a first injection
Antibody testing was performed in all 16 patients with CML. The presence of IgG to Spike and plasma neutralising activity was measured 3 weeks after the first vaccine injection [median (IQR) 21 (21-27Á25) days]. A positive anti-S IgG ELISA response was seen in 87Á5% (14/16) of patients analysed after a first injection, with only two patients showing undetectable IgG to Spike at 1:25 dilution (Table I and Fig 1A). Of the two patients with a negative serological response, one had previously been investigated for potential immune suppression and recurrent infections, whilst the other was on second-line treatment with ponatinib, with suboptimal response.
The median (IQR) EC 50 value for anti-S IgG in all patients from ELISA testing was 100 5 (25-408Á3). Amongst different TKIs the median EC 50 values were 251 5 for imatinib, 100Á5 for nilotinib, 373Á5 for dasatinib, 379Á5 for bosutinib and 25 for ponatinib. No patients had evidence of confirmed previous infection as determined by a >fourfold increase in OD of IgG against the Nucleocapsid (N) and S protein in the pre-vaccine sample. 4 However, a single patient did have a weakly positive anti-S IgG EC 50 , as well as a mildly raised anti-N OD on a pre-vaccine sample, suggestive of possible previous infection.

T-cell response to first injection of BNT162b2
The induction of virus-specific T-cell responses by BNT162b2 vaccination was assessed directly ex vivo by flow cytometric enumeration of antigen-specific CD8 + and CD4 + T lymphocytes using an intracellular cytokine assay for IFN-c, TNF-a and IL-2. Before vaccination, T-cell analysis was performed in eight patients, with only one patient showing evidence of a monofunctional CD4 + T-cell response to the S protein with expression of IFN-c (Table I).
After a first injection of BNT162b2, T-cell analysis was performed in 15 patients. A response was considered to be positive if there was a threefold increase in any proinflammatory cytokine from baseline expression, and above a threshold of 0 01. A memory T-cell response was seen in 14 out of 15 evaluable patients (93Á3%), with the only patient not showing a T-cell response being post allogeneic haematopoietic stem cell transplantation (HSCT) and taking ponatinib (Table I and Fig 2). A SARS-CoV-2 specific CD4 + T-cell response was seen in 80% (12/15) and a SARS-CoV-2 specific CD8 + T-cell response was seen in 60% (nine of 15, Table I and Fig 2). A polyfunctional cytokine response in either CD4 or CD8 + T cells was seen in 80% (12/15) of patients, with a polyfunctional CD4 + response in 60% (nine of 15) and a polyfunctional CD8 + T-cell response in 40% (six of 15) (Fig 2).

Discussion
Large international randomised placebo-controlled studies have shown the efficacy of the BNT162b2 vaccine, with a two-dose regime resulting in a 95% reduction in cases in the general population. 5 Evidence of a protective immune response to a single dose is shown by a reduction in cases of 52% reported in the interim between first and second doses in those receiving BNT162b2. 5 Sahin et al. 6 reported a detailed analysis of the immune response to BNT162b2 in healthy controls, with a Th1 skewed CD4 + T-cell response in 95Á2% and a CD8 + T-cell response in 76Á2%, as determined by Elispot testing. They also described antibody responses to vaccination that were significantly greater than those observed in a group of patients who had recovered from SARS-CoV-2 infection. 6 T-cell immunity may prove to be particularly important for protection from SARS-CoV-2, with the evidence from the SARS-CoV-1 epidemic showing that antibody responses were relatively short-lived following infection, whilst memory T-cell responses were significantly more durable. 7 Our group has recently reported a significant decline in neutralising antibody levels in the 3 months after infection with SARS-CoV-2. 3 We have also reported that robust T-cell responses can be observed as long as 6 months after infection with SARS-CoV-2 in a small cohort of patients with chronic myeloproliferative Table II. Injection-site and systemic adverse effects after receiving the vaccine among patients.

Patient number
Age, years neoplasms including CML. 8 Furthermore, a number of additional studies have elegantly demonstrated the T-cell response to SARS-CoV-2 in the general population. [9][10][11][12][13] However, a recently submitted report describes a significantly reduced immune response in a heterogeneous group of patients with solid and haematological malignancies, 1 bringing concerns over the ability of clinically vulnerable patients with haematological malignancies to mount a protective response following a single dose of SARS-CoV-2 BNT162b2 vaccination.
Among patients with chronic myeloid malignancies, TKI therapy is recognised to cause variable immune deficiency, with TKIs that also inhibit Src family kinases causing significant T-cell dysfunction due to the pivotal role that these kinases play in signalling downstream from the T-cell receptor. 14 We have previously shown that B-cell function is also impaired by TKI therapy through off target inhibition of Btk, a kinase that is important for normal B-cell signalling, leading to reduced efficacy of the seasonal influenza vaccination. 2 However, during the influenza A virus subtype H1N1 (H1N1) vaccination campaign, we demonstrated that the seroprotection rate to a first injection of 2009 H1N1 vaccine [Pandemrix; GlaxoSmithKline (GSK) plc, Brentford, Middlesex, UK] was not significantly different between patients with chronic phase CML and healthy controls, unlike other haematological conditions such as B-cell malignancies or recipients of HSCT. 15 Consistent with our previous experience in H1N1 and seasonal influenza vaccination, our data show encouraging results, with 87Á5% seroconversion to a first SARS-CoV-2 BNT162b2 injection in patients with CML, contrasting with what has been described in the first report of vaccination in patients with cancer. 1 In addition, nearly all the patients with CML in our present analysis demonstrated both mono-and polyfunctional T-cell cytokine responses to SARS-CoV-2, a response that is similar to healthy controls tested in previous trials of BNT162b2 vaccination, 6 although it should be noted that methodology differs between studies. Overall, both seroconversion and T-cell response to a single injection demonstrate the immunogenicity of SARS-CoV-2 BNT162b2 in patients with CML, with neutralising antibodies responses seen in all patients. To our knowledge the present report is the first of humoral and T-cell response to vaccination against SARS-CoV-2 in patients with CML taking TKIs. These data are particularly important in the context of the decision from the DHSC to increase the interval between a first and a second vaccine injection, and demonstrate that patients with CML taking TKIs receive significant protection from a first injection of SARS-CoV-2 BNT162b2.
Finally, we found that patients taking nilotinib had a significantly greater increase in TNF-a and dual TNF-a/IFN-c expression in SARS-CoV-2 specific CD4 + cells, when compared with patients taking other TKIs. This suggests that the highly selective ABL1 TKI nilotinib, which does not inhibit Src kinases or other kinases important to the immune response, may have less effect on the patients' immune system. However, it is not possible to draw definitive conclusions on the effect of different TKIs from this relatively small cohort.
Further prospective data are required to confirm that the immune response to vaccination we have described in the present study translates into a reduction in SARS-CoV-2 infections in this patient group. In addition, longitudinal studies are required to characterise the response to the twodose vaccination regimen, as a second injection may provide a stronger and longer lasting protection. Additional studies will need to determine if the immune response will be sufficient to protect against emerging variants, as well as analyse the effect of other currently available and emerging vaccines against SARS-CoV-2.