Post-transplant cyclophosphamide for unrelated donor peripheral blood stem cell transplant with special attention to graft content and the impact of a higher γδ T cell dose

doi:10.21203/rs.3.rs-2579840/v1

In this study, PtCy was used in 44 patients along with mycophenolate and tacrolimus with HLA matched (29) and mismatched (15) unrelated. The study was done to determine the impact of graft content on outcome thus all patients had flow cytometric analysis of their graft content including the number of B cells, NK cells, and various T cell subsets. Of the 15 patients with HLA mismatched donors, 12 were one antigen mismatched and 3 were 2 antigen mismatched. Sixteen (36.3%) of the patients developed acute GVHD (without any grade IV acute GVHD). For all patients the median time to ANC engraftment was 18 days while median time to platelet engraftment was 24 days. Mean estimated overall survival was 59.9 months, median overall survival was not reached. Higher γδ T cell dose was associated with the development of acute GVHD (p=0.0038). The use of PtCy in addition to MMF and tacrolimus has been shown to be a reasonable strategy to successfully engraft with unrelated donors. This method, potentially with the added intervention of selective gamma-delta T cell depletion, could increase transplant feasibility in recipient-donor combinations with greater HLA disparity and ensure that ethnic minorities have greater access to stem cell transplants.

Health sciences/Medical research/Translational research

Health sciences/Diseases/Haematological diseases/Haematological cancer/Leukaemia/Acute myeloid leukaemia

Biological sciences/Stem cells/Haematopoietic stem cells

Multple studies have shown that when given early after stem cell infusion, post transplant cyclophosphamide (PtCy) causes functional impairment of alloreactive T cells and induces expansion of regulatory T cells, which are thought to be a major contributor to the development of graft versus host disease (GVHD).^{1, 2, 3, 4}

One large study that supports this conclusion is a recent phase III study (HOVON-96 Trial) that showed the use of PtCy increased the percentage of patients who survive without severe GVHD.³ In that trial, patients received peripheral blood stem cells from 8/8 matched related and unrelated donors and were randomized to recieive cyclopsporine (CSA) and mycophenoplate mofetil (MMF) for acute GVHD prophylaxis or PtCy and CSA. The cumulative incidence of acute GVHD grades II-IV at 6 months was 48% in the CSA/MMF group and 30% in the CSA/PtCy group. The cumulative incidence of chronic GVHD at 2 years was 48% in the CSA/MMF group and 16% in the CSA/PtCy group. The 1 year estimate of GVHD/relapse free survival was 21% in the first group and 45% in the second group. All of these differences were statistically significant.³ A National Marrow Donor Program (NMDP) Sponsored Phase II clinical trial with PtCy and using bone marrow as the stem cell source source from 80 HLA mismatched unrelated donors found an overall survival of 76% with a acute GVHD grade II-IV rate of 43% (myeloablative conditioning) and a 33% rate (reduced intensity conditioning) at day + 100. ⁵

Similar results have been reported in BMT CTN 1203 and 1703 but those studies and HOVON-96 were almost exclusively composed of patient receiving reduced intensity transplants that might result in less GVHD than myeloablative transplants.^{5, 6, 7}

This current study was designed to evaluate the use of PtCy in addition to tacrolimus and MMF in patients receiving mobilized stem cells procured from the peripheral blood of unrelated donors in a myeloablative and a reduced intensity setting. This study aimed to look at what impact specific cell populations in the graft may have on transplant outcome. Patients who were transplanted with HLA-matched as well as HLA-mismatched unrelated donor stem cells were included. We hypothesized that including mismatched unrelated donors, if shown to have similar outcomes as previous studies, would encourage future studies to allow a higher degree of HLA disparity between donors and recipientsas is being evaluated in the ACCESS trial. This would enable more patients, who would otherwise have not been able to receive stem cell transplant owing to the lack of HLA-matched unrelated donors, to find donors, and could potentially lead to improved long term outcomes with increased graft-versus-tumor effects from these mismatched donors. In this study, the survival characteristics, cumulative incidence of both acute and chronic GVHD, engraftment parameters as well as the influence of graft content on outcomes is reported.

Patients:

Patietns were enrolled in this clinical trial from 2011 through 2019 by having diseases in which allogeneic transplantation from an unrelated donor was thought to be beneficial. Major entry criteria included the diagnosis of a hematologic malignancy and adequate organ function as defined by an adjusted diffusion capacity ≥ 45%, left ventricular ejection fraction of ≥ 45%, creatinine clearance of ≥ 60 ml/min, total bilirubin ≤ 1.8 mg/dL, AST and ALT ≤ 2.5 X upper limit of normal, and Karnofsky Performance Status of ≥ 80%. All patients underwent transplant from an unrelated donor. The primary endpoints of the trial were the cumulative incidences of acute and chronic GVHD. The secondary endpoints were incidences of primary graft failure and overall survival (OS). Followup was current as of 2021. The study was approved by the Institutional Review Board, and all patients signed informed consent.

Definitions

Acute GVHD was defined using the Glucksberg criteria.⁸ Chronic GVHD was defined using the National Institutes of Health (NIH) Consensus Conference guidelines.⁹ The hematopoietic cell transplantation-specific comorbidity index (HCTI) was used for risk stratification¹⁰ as was the revised disease risk index (RDRI).¹¹

Conditioning:

Pre-transplant conditioning was either a myeloablative conditioning regimen (MAC, 12 Gy TBI) or reduced intensity conditioning regimen (RIC, fludarabine, 2 Gy TBI and thiotepa or busulfan). All patients underwent a T-cell replete HSCT after receiving MAC or RIC conditioning regimen. GM-CSF was administered starting on day + 5 and continued until neutrophil recovery. All patients received prophylaxis against fungal, herpetic and encapsulated organism infections. The MAC regimen is shown in Table 1 and RIC regimen is shown in Table 2. Twenty one patients underwent MAC and 23 received RIC. The initial 4 patients who received RIC received thiotepa in addition to fludarabine and TBI. Due to a nationwide shortage of thiotepa in 2015 this was switched to busulfan which was given to the subsequent 19 patients.

GVHD Prophylaxis:

GVHD prophylaxis consisted of PtCy, tacrolimus, and MMF. Patients received two doses of cyclophosphamide 60 mg/kg IV daily starting day + 3. This Cy dosing rather than 50mg/kg x 2 has been used at TJU since 2006 because Cy was not used as part of the conditioning regimen as it was at other institutions originally. MESNA (sodium-2-mercaptoethane sulfonate) was administered as a 60 mg/kg/continuous IV infusion over 24 hours starting 30 minutes prior to cyclophosphamide infusion and ending 24 hours after the last dose of cyclophosphamide. MMF was administered at a dose of 1 gram IV twice daily beginning on day + 5. This was discontinued on day + 28 in the absence of GVHD. Tacrolimus was started on day + 5 and dose was titrated to maintain a target level of 8 ng/ml +/- 2. Tacrolimus tapering was initiated on day + 42 in the absence of acute GVHD.

Engraftment and Donor Chimerism:

All unrelated donor products were non-cryopreserved. Neutrophil recovery was defined as the first of 3 consecutive days with an absolute neutrophil count (ANC) greater than 0.5 × 10⁹/L. Platelet recovery was defined as a platelet count greater than 20 × 10⁹/L without platelet transfusion in the preceding 7 days. Donor chimerism was assessed on or about day + 28, +90, + 180, +270, and + 365 while lymphocyte subsets as measured by flow cytometry were assessed on or about days + 28 and day + 90. Primary graft failure was defined as a lack of neutrophil recovery in the absence of progressive malignancy. Secondary graft failure was defined as loss of donor engraftment in the absence of progressive malignancy.

CMV prophylaxis:

Patients who were CMV seropositive were monitored by weekly PCR testing and treated premptively through 2017. Patients who were CMV seropositive and transplanted in the years 2018 and 2019 (8 patients) received letermovir for CMV prophylaxis and were still monitored weekly.

Transfusion support:

Packed red blood cell transfusions were given as necessary to keep the hemoglobin ≥ 8 g/L. A higher hemoglobin (≈ 10g/L) was maintained during cyclophosphamide administration per TJUH BMT program guidelines. Platelet transfusions were used as needed to keep the count ≥ 10x10e9/L, with ≥ 20x10e9/L used for situations with an excessive bleeding risk and ≥ 50x10e9/L used for acute bleeding events.

Statistical analysis:

Survival and estimates to time to GVHD were calculated using Kaplan-meier survival functions. Comparisons of survival and GVHD incidence as it relates to graft content were calculated using log rank and Gray’s testing.¹²

Patient Characteristics:

Patient characteristics are shown in Table 3. In terms of the Revised Disease index 5 (11%) had a score of 0 (low risk) 25 (57%) had a score of 1 (intermediate risk) and 14 (32%) had a score of 2 (high risk).

Survival and Relapse Outcomes:

There were 15 total deaths recorded with a median followup of 70.2 months. Mean estimated overall survival (OS) was 59.9 months (95% CI 47.2–72.5) with a total of 3 deaths prior to 1 year. Median OS was not reached. At 2 years, 13 patients had died (29.5%) with an estimated 2 year OS of 67.4%. Of these 15 deaths, 5 died of relapse, 5 of infection (none of which were GVHD related), 1 of a gastrointestinal bleed, 1 of lung cancer, 1 of venoocclusive disease along with graft failure, and 1 of respiratory failure due to an unknown cause. Of note one patient developed CML from donor cells. Kaplan-Meier curve for OS is shown in Fig. 1. A total of 9 (20.4%) patients relapsed with a median time to relapse of 277 days (89-2300). Of them, 6 relapsed within a year after transplantation.

Engraftment, Product, and HLA Information:

Median time to ANC engraftment was 18 (range 12–28) days while median time to platelet engraftment was 24 (range 16–79) days. Out of the 44 patients, 1 had primary graft rejection. Mean CD4 + cells/µL and CD8 + cells/ µL at day 28 and 90 are listed in Table 4. Median T cell dose was 2.90 x 10⁸ (range 1.30–4.40 x 10⁸) cells/kg. Twenty six patients received a T cell dose of < 3.0 x 10⁸ cells/kg (lower T cell dose, LTCD), with an estimated mean OS of 61.5 months (95% CI 44.7–78.3) while 18 patients who received a T cell dose of ≥ 3.0 x 10⁸/kg (higher T Cell dose, HTCD) had an estimated mean OS of 48.9 months (95% CI 33.9–63.8). This difference was not statistically significant (log rank, p = 0.880). Median CD34 + dose was 8.10 x 10⁶ cells/kg (3.00–10.00). 11 patients received a CD34 + dose of < 6.0 x 10⁶ cells/kg (lower CD34 + dose, LCD),with a mean estimated OS of 59.7 months (95%CI 35.7–83.7) while 33 patients received a CD34 + dose of ≥ 6.0 x 10⁶ cells/kg (higher CD34 + dose, HCD), with a mean estimated OS of 60.1 months (95% CI 45.6–74.7). This difference was not statisticaly significant (log rank, p = 0.893). If patients were HLA matched, their mean estimated OS was 56.4 months (95% CI 40.5–72.3) while if they were unmatched their mean estimated OS was 65.9 months (95% CI 45.9–85.9). This difference was not statistically significant (log rank, p = 0.409). There was one incidence of graft failure in a patient who was transplanted for primary myelofibrosis who eventually developed venooclusive disease before dying.

Graft-versus-Host Disease:

36.3% (16) of patients developed acute GVHD, 13.6% (6) of whom had grade I, 13.6% (6) had grade II and 9.1% (4) had grade III. There were no incidences of grade IV acute GVHD. Of the 16 patients who had acute GVHD, 10 had skin only, 2 had gastrointestinal only, 1 had liver only and 3 had skin and gastrointestinal GVHD. 18.1% (8) patients developed chronic GVHD, of which 2 had lung/skin, 2 had oral/ocular, 1 had oral/lung, 1 had oral/liver, 1 had skin/lung and 1 had skin/ocular. Acute and chronic GVHD cumulative incidence curves are shown in Fig. 2. GVHD free survival probability is shown in Fig. 3. Acute GVHD cumulative incidence was not statistically different if patients were HLA matched or mismatched (Fig. 4, Gray’s test, p = 0.64).

OS as it related to development of acute GVHD or chronic GVHD was not found to be significantly different (log rank, p = 0.421 and p = 0.124 respectively). The number of the following cell types in the graft were determined by flow cytometry analysis using the following cell surface markers: CD3+/CD8+, CD3+/CD4+, CD19+, CD56+, αβ T cells, and γδ T cells to determine the impact on acute and chronic GVHD incidence. The number of only one cell type was found to have an impact on GVHD incidence. Using the median value (9.8 x 10⁶/per ul) as a cut-off, a higher γδ T cell dose was correlated with acute GVHD (p = 0.0038, Fig. 5). It was seen that out of the 8 patients who developed chronic GVHD, 6 of them received a γδ T cell dose above the median however this difference was not found to be significant but this is limited by the small sample size and low incidence of chronic GVHD. Relapse was not significantly different between patients who received a γδ cell dose above the median versus those who received a γδ cell dose below the median (p = 0.7973, Fig. 6).

CMV Status:

Of the 44 patients, 26 were seropositive for CMV pre-transplant, of which 14 had CMV reactivation within the first 100 days post HSCT with a mean of 90.4 days after HSCT to CMV reactivation. One patient had developed CMV DNAemia more than 100 days after HSCT. For the 14 patients who had CMV reactivation within 100 days of HSCT, their mean estimated OS was 33.8 months (95% CI 26.0-41.6) while in those who did not have CMV re-activate their mean estimated OS was 42.7 months (95% CI 30.9–54.5). Four of the patients who reactived within 100 days after HSCT and after 2017, all did so while taking letermovir.

In this study, we found successful engraftment following PtCy in unrelated HLA matched and mismatched patients with only 1 out of 44 grafts failing. Median time to ANC engraftment was 18 days while median time to platelet engraftment was 24 days. This is similar to previous results of PtCy studies. In a study done by Mehta et al, they found that in their PtCy, tacrolimus, and MMF GVHD prophylaxis group, median time to neutrophil engraftment was 18 days while median time to platelet engraftment was 25.5 days.¹³ Additionally, a study done by Holitick et al found that median time to neutrophil engraftment was 21 days while time to platelet engraftment was 18 days.¹⁴ This latter study only used PtCy as GVHD prophylaxis. The HOVON-96 trial did not report engraftment parameters.³ The NMDP trial reported median engraftment times of 17 or 18 days for neutrophils and 33 or 35 days for platelets (the two values were for myeloablative conditioning and reduced intensity conditioning respectively).⁵ This study shows similar engraftment times for both neutrophils and platelets with a low incidence of graft rejection suggesting successful engraftment following both HLA matched and mismatched unrelated donor transplant (at least for 1 antigen mismatches).

In terms of immunologic recovery, in a study done by Bogdanov et al PtCy was associated with a mean CD4 + count of 94 cells/µL at month 1 and 116 cells/µL at 3 months.¹⁵ We found similar results with our mean CD4 + counts at day + 28 being 94.5 cells/µL but higher CD4 + counts at day + 90 at 176.5. T cell dosing was not published in this study but it was found that mean CD34 + dose was 6.3 x10⁶.¹⁵ Our mean CD34 + dose was higher at 7.86 x 10⁶ which may have accounted for the higher CD4 + counts at day + 90.

In terms of GVHD, 16 of 44 patients (36.3%) developed acute GVHD while 8 (18.2%) of the patients developed chronic GVHD. Within the first 100 days, cumulative incidence of acute GVHD was 31.8% while at 1 year cumulative incidence of chronic GVHD was 15.9%. Cumulative GVHD incidence was not significantly different between HLA matched and mismatched donors thus in this study the PtCy had a neutralizing effect on the incidence of GVHD with 1 HLA antigen mismatched unrelated donors. A study done by Mielcarek et al looking at HLA matched related and unrelated donors analyzed CSA in addition to PTCy and showed a cumulative incidence of acute GVHD grade 2–4 in the first 100 days was 77% with none having grade 3 or 4 and a cumulative incidence of chronic GVHD of 16% at 1 year.¹⁶ The significantly higher rate of acute GVHD in the Mielcarek study as compared to this study suggests that the combination of PT-Cy, MMF and Tacrolimus may be a more effective prevention strategy than PTCy and CSA alone. Additionally, the cumulative incidence of acute GVHD at 18 months in the PtCY arm of the HOVON-96 trial was 30% which is similar to what was observed in this study.³ In the NMDP trial the acute GVHD rate II-IV in the reduced intensity arm was 33% and in the myeloablative arm it was 43%. The NMPD trial was mostly composed of patients that were a one or two antigen mismatch while this trial was mainly HLA matched or one antigen mismatched. ⁴

In the HOVON-96 trial the chronic GVHD incidence at 2 years was 16% and in the NMDP study it was 18% at one year with reduced intensity conditioning and 36% with myeloablative conditioning. ^3,5 In the HOVON-96 study, patients received transplants from either a matched sibling donor or a matched unrelated donor, no mismatched unrelated donors were used. This study shows similar or improved rates of both acute and chronic GVHD in PtCy transplant recipients making our method of using matched and mismatched unrelated donors feasible from a GVHD standpoint and was reflected in the Phase II NMDP trial. ⁵

One interesting aspect of this study was the focus on the cellular composition of the graft as it related to outcome. We found that a higher γδ T cell dose was associated with increased incidence of acute GVHD. In experimental models of acute GVHD, infusion of donor γδ T cells increased acute GVHD and absence of host γδ T cells was associated with reduced antigen presenting cell activation and acute GVHD.¹⁷ This correlates with a study done by Pabst et al using PtCy and methotrexate as GVHD prophlayxis and HLA matched unrelated donor transplants which found that an increased graft concentration of γδ T cells was significantly associated with the occurrence of acute GVHD.¹⁸ In general, γδ T cells are involved in the response to pathogenic stimuli. They develop in the thymus and express a rearranged TCR consisting of a TCR-γ and TCR-δ chain. Upon activation, γδ T cells can produce a large amount of cytokines consisting of interferon-γ and tumor necrosis factor-α.¹⁹ This cytokine release may contribute to the development of acute GVHD. In support of this, it has been shown that infusing γδ T cells into mice has been shown to induce lethal acute GVHD though this has never been proven in humans.²⁰ γδ T cells have both anti tumor and protumor properties²¹ and with a better understanding of the subsets of these cells or how the use of certain cytokines influence their function, it may be possible to improve the antitumor property of the graft. It may also be possible that as the degree of HLA mismatch increases and as does the risk of acute GVHD, it might be useful to consider “reducing” the γδ T cell dose.

Limitations of this study include its small sample size. Estimates of median OS were not possible as 50% of patients had not died by the data collection point. Additionally, due to a small sample size some “differences” evaluated were not significant in terms of influencing survival when they may have been if applied to a larger population and vice versa. Lastly, the study was weighted towards better risk patients with higher KPS and lower HCT-CI. The small sample size does not negate the value of they study as it is one of the first to look closlely at graft content and possible influence on outcome. It also includes patients receiving myeloablative transplants. Once could argue that the comparison between two groups in the study (interms of degree of HLA mismatch) is not optimal but there is no larger data set with detailed graft content to compare to with post transplant cyclophosphamide.

Another issue is the heterogeneous nature of the treatment however there are also limations to larger studies such as HOVON-96, BMT CTN 1203 and BMT CTN 1703 which had few if any patients treated with myeloablative(MA) regimens and at least one study has associated the use of MA regimens with an increased risk of GVHD. ^5,6,7 Also none of these studies looked at the possible contributions of graft content to outcome. Also there are potentially advantages to further reductions of GVHD even in transplanst from matched unelated donors.

This study shows the feasibility of both unrelated matched and and 1 antigen- mismatched HSCT with PT-Cy in terms of OS, GVHD occurrence and engraftment parameters as shown by others and also suggests CD3 + and γδ T cell dosing should be evaluated in future studies and could include the use of selective γδ T cell depletion or simply giving less of the product (if the CD34 cell dose is adequate) or increasing the amount of immunosuppression which could allow a higher degree of HLA disparity without increasing the risk of GVHD. Using more mismatched unrelated donors could enfranchise more patients who would otherwise not be eligible for HSCT and is currently a focus of ongoing trials such as the ACCESS trial. Future studies should include more information on graft content. Results from larger trials which if reflected the same conclusions as this study could lead to further investigation as to whether reduction of γδ T cell dose could lead to improved outcome.

Acknowledgments:

The authors wish to thank Shannon Rudolph for data gathering.

Author Contributions:

The manuscript was written by C.J. B.L. provided all the statistical calculations. S.R.

assisted with the data collection. JLW was the PI for the clincal trial, contributed

patients to the trial, revised the text and oversaw the entire process. All others

contributed to the revision of the text and/or contributed patients to the clinical trial.

O’Donnell PV, Luznik L, Jones RJ, et al. Nonmyeloablative bone marrow transplantation from partially HLA-mismatched related donors using posttransplantation cyclophosphamide. Biol Blood Marrow Transplant. 2002; 8:377-86.
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Table 1

	-3	-2	-1	0	+1	+2	+3	+4	+5
AM	TBI 1.5 Gy	TBI 1.5 Gy	TBI 1.5 Gy	TBI 1.5 Gy	Rest	Rest	CY 60 mg/kg	CY 60 mg/kg	Rest Start Tacro & MMF
PM	TBI 1.5 Gy	TBI 1.5 Gy	TBI 1.5 Gy	TBI 1.5 Gy	Rest	Rest	CY 60 mg/kg	CY 60 mg/kg	Rest Start Tacro & MMF
				PBSC Infusion

TBI- Total Body Irradiation; CY- Cyclophosphamide; Tacro- Tacrolimus; MMF- Mycophenolate Mofetil; PBSC- Peripheral Blood Stem Cells

Table 2

Day
-5	-4	-3	-2	-1	0	+3	+4	+5
Fludarabine 30 mg/m2	Fludarabine 30 mg/m2	Fludarabine 30 mg/m2	Fludarabine 30 mg/m2	Rest	TBI 2 Gy	CY 60 mg/kg	CY 60 mg/kg	Rest Start Tacro & MMF
	Busulfan 3.2 mg/kg* or	Busulfan 3.2 mg/kg* or		Rest	TBI 2 Gy	CY 60 mg/kg	CY 60 mg/kg	Rest Start Tacro & MMF
Or Thiotepa 5 mg/kg* (Instead of Busulfan)	Thiotepa 5 mg/kg*	Thiotepa 5 mg/kg*
					PBSC Infusion

TBI- Total Body Irradiation; CY- Cyclophoshamide; Tacro- Tacrolimus; MMF- Mycophenolate Mofetil; PBSC- Peripheral Blood Stem Cells;
*In 2015, Thiotepa was switched to Busulfan due to nationwide shortage. 4 patients received Thiotepa and 19 received Busulfan.

Table 3

Parameter
Age, median (range)	60.0 (19-73)
Gender
Male	70.5% (31)
Female	29.5% (13)
Race/Ethnicity
Caucasian	73.3% (32)
Non-Caucasian	27.7% (12)
Diagnosis
AML	27.3% (12)
MDS	22.7% (10)
Transformed DLBCL	11.4% (5)
MPD	6.8% (3)
PH+ ALL	6.8% (3)
CML	4.5% (2)
B Cell ALL	4.5% (2)
Multiple Myeloma	4.5% (2)
Mantle Cell Lymphoma	4.5% (2)
Aplastic Anemia	2.3% (1)
Primary DLBCL	2.3% (1)
T Cell NHL	2.3% (1)
HCT-CI (Mean)	2.48
Revised Disease Risk Index (Mean)	1.20
Disease at Transplant?
Yes	47.7% (21)
No	52.3% (23)
Conditioning
RIC	52.3% (23)
MAC	47.7% (21)
HLA Status
Matched	65.9% (29)
Mismatched	34.0% (15, 12 one antigen mismatched, 3 two antigen mismatched)

AML- Acute Myeloid Leukemia; MDS- Myelodysplastic Syndrome, DLBCL- Diffuse Large B Cell Lymphoma; MPD- Myeloproliferative Disease; PH- Philadelphia Chromosome; ALL- Acute Lymphoid Leukemia; CML- Chronic Myelogenous Leukemia; NHL- Non-Hodgkin’s Lymphoma; HCT-CI- Hematopoietic Cell Transplant-Comorbidity Index; RDRI- Revised Disease Risk Index; HLA- Human Leukocyte Antigen

Table 4

Cell Counts Day +28	Mean, Cells/µL (Range)
CD3/CD4+	94.5 (11.4-482.0)
CD3/CD8+	232.1 (7.0-4539.0)
Cell Counts Day +90
CD3/CD4+	176.5 (19.0-621.0)
CD3/CD8+	523.4 (14.7-4321.0)

The authors have declared there is NO conflict of interest to disclose.

Post-transplant cyclophosphamide for unrelated donor peripheral blood stem cell transplant with special attention to graft content and the impact of a higher γδ T cell dose

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Abstract

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Statistical analysis:

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