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\begin{document}

\title{Delayed but Successful T Cell Immune Reconstitution Following Umbilical
Cord Blood Transplantation Conditioned with Thymoglobulin alone in
IL-7R\selectlanguage{greek}α-\selectlanguage{english}mutated SCID\selectlanguage{english}}



\author[1]{Eman Al-Antary}%
\author[1]{Mary Caverly}%
\author[1]{Steve Buck}%
\author[2]{Sharat Chandra}%
\author[1]{Sureyya Savasan}%
\affil[1]{Children's Hospital of Michigan}%
\affil[2]{Cincinnati Children's Hospital Medical Center Division of Bone Marrow Transplantation and Immune Deficiency}%


\vspace{-1em}



  
  \date{May 25, 2024}


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\selectlanguage{greek}\textbf{Delayed but Successful T Cell Immune Reconstitution Following
Umbilical Cord Blood Transplantation Conditioned with Thymoglobulin
alone in IL-7Rα-mutated SCID}\selectlanguage{english}

Eman T. Al-Antary, MD\textsuperscript{1,5}, Mary Caverly,
CPNP\textsuperscript{2}, Steve Buck\textsuperscript{3,} Sharat Chandra,
MD\textsuperscript{4}, S\selectlanguage{ngerman}üreyya Sava\selectlanguage{polish}ş\selectlanguage{english}an, MD\textsuperscript{1-3, 5}

\emph{\textsuperscript{1}Chidren's Hospital of Michigan, Division of
Hematology/Oncology, Detroit, Michigan}

\emph{\textsuperscript{2}Children's Hospital of Michigan, Division of
Hematology/Oncology, Pediatric Blood and Marrow Transplantation Program,
Barbara Ann Karmanos Cancer Center, Detroit, Michigan}

\emph{\textsuperscript{3}Children's Hospital of Michigan, Division of
Hematology/Oncology, Flow Cytometry Laboratory}

\emph{\textsuperscript{4} Division of Bone Marrow Transplantation and
Immune Deficiency, Cincinnati Children's Hospital} \emph{Medical Center,
Department of Pediatrics, University of Cincinnati School of Medicine}

\emph{\textsuperscript{5}Department of Pediatrics, Central Michigan
University College of Medicine, Mt Clemons, Michigan}

\textbf{Correspondence} :

S\selectlanguage{ngerman}üreyya Sava\selectlanguage{polish}ş\selectlanguage{english}an, MD

Children's Hospital of Michigan

Hematology/Oncology

Pediatric Blood and Marrow Transplantation Program

3901 Beaubien Blvd.

Detroit, MI 48201

Phone: 313-745-5516

Fax: 313-745-2357

E-mail: ssavasan@med.wayne.edu

\textbf{Conflict of Interest Statement:} Authors declare no conflict of
interest and no funding for this manuscript

\textbf{Word count (main Text):} 840

\textbf{Tables:} 0

\textbf{Figures:} 1

\textbf{Supplemental files:} 0

\textbf{References:} 13

\textbf{Key words} : IL-7R\selectlanguage{greek}α-\selectlanguage{english}mutation SCID, Thymoglobulin, umbilical cord
blood transplant, Covid-19 infection, delayed T-cell recovery

\textbf{Running title} : T cell reconstitution in IL-7R\selectlanguage{greek}α-\selectlanguage{english}mutated SCID
after UCBT\selectlanguage{english}
\begin{longtable}[]{@{}ll@{}}
\toprule
\textbf{Abbreviations} & \textbf{Full phrase}\tabularnewline
\midrule
\endhead
SCID & Severe combined immunodeficiency disorder\tabularnewline
IL-7R\selectlanguage{greek}α & Interleukin-7 receptor-alpha\tabularnewline
HSCT & Hematopoietic stem cell transplantation\tabularnewline
IVIG & Immunoglobulin\tabularnewline
HLA & Human leukocyte antigen\tabularnewline
UCBT & Umbilical cord blood transplantation\tabularnewline
TREC & T cell receptor excised circles\tabularnewline
rATG & Rabbit anti-thymocyte globulin\tabularnewline
GvHD & Graft versus host disease\tabularnewline
RTE & Recent thymic emigrant population\tabularnewline
STR & Short tandem repeat\tabularnewline
\bottomrule
\end{longtable}

\textbf{To the Editor,}

Severe combined immunodeficiency disorder (SCID) due to mutation in
interleukin-7 receptor-alpha (IL-7R\selectlanguage{greek}α\selectlanguage{english}) gene resulting in B+NK+ phenotype
can be successfully treated with hematopoietic stem cell transplantation
(HSCT) {[}1, 2{]}. NK+ SCID cases have been challenging due to risk of
graft rejection mediated by NK cells. We report an outcome of a baby
with IL-7R\selectlanguage{greek}α-\selectlanguage{english}mutated SCID who underwent umbilical cord blood
transplantation (UCBT) with anti-thymocyte globulin alone conditioning.

A male patient with B+NK+ SCID secondary to homozygous \emph{IL7R} \selectlanguage{greek}α
\selectlanguage{english}exon 1 deletion underwent UCBT at 3 months of age. There was no evidence
of maternal engraftment. Matched sibling or unrelated donors were not
available, and parents opted UBCT over haploidentical SCT. The patient
received molecularly HLA 7/8-matched (C allele mismatch) UCBT at a total
nucleated cell dose of 15.6x10\textsuperscript{8}/kg and CD34+ dose of
2.43x10\textsuperscript{6}/kg conditioned with Thymoglobulin\selectlanguage{ngerman}® (rabbit
anti-thymocyte globulin) (rATG) at a total dose of 7.5mg/kg (days -4
thru -2). For graft versus host disease (GvHD) prophylaxis, he was given
mycophenolate mofetil (days 0- thru +35) and tacrolimus day -3 through
day +57 at which time he had no evidence of engraftment.

Due to lack of any T cell recovery at 4 months post-UCBT, keeping the
possibility of UCB donor T cell depletion from rATG in mind, proceeding
with a second transplant option was debated. However, he was noted to
have evidence of T cell recovery (absolute CD3+ count of 98 cells/mcL
with 6.6\% CD4+ naïve T cells) five months post-UCBT, which continued to
improve over time.

Engraftment and immune reconstitution were monitored by flow cytometric
immune profiling and recent thymic emigrant population (RTE)
determination characterized by CD31+/CD4+ naïve T cells, T cell receptor
excision circles (TREC) analysis, short tandem repeat (STR) studies in
myeloid and lymphoid populations, serum immunoglobulin levels and
mitogen response assessments (Figure 1). Serum IgA and IgM levels were
detected at 16 and 83 mg/dl, respectively on day +183. Absolute
lymphocyte counts, T cell numbers, RTE percent and serum IgG, IgA, IgM
levels all increased and reached normal levels by day +273; last
intravenous immunoglobulin (IVIG) supplementation was on day +183. While
myeloid chimerism was 0\%, B-cell donor chimerism increased
progressively to a maximum of 41\% and NK cells at 21\% donor chimerism
on day +217 post UCBT. Following T-cell recovery, the patient maintained
full donor chimerism in T cells (98\% on day +518). Interestingly,
higher CD5-dim T cell percent, seen during early days of RTE
observation; however, had declined later. T cells have shown almost
normal mitogen responses at day+248 (Figure 1). Subsequently,
anti-microbial prophylaxis was discontinued. The patient is now 25
months post-UCBT and is doing well. He did not develop GvHD. He has been
growing and developing age-appropriately and has started childhood
immunizations.

This is the first reported case of a successful UCBT for IL-7R\selectlanguage{greek}α-\selectlanguage{english}mutated
SCID conditioned with rATG alone. The patient achieved full donor T cell
chimerism along with normal quantitative and qualitative T and B cell
function. Our experience suggests that conditioning with rATG in the
setting of UCBT may lead to delayed T cell recovery likely due
to\emph{in-vivo} presence of rATG at the time of UCBT infusion leading
to depletion of T cells in the UCB graft. Admiraal \emph{et al.} also
showed that T cell reconstitution was dependent on ATG exposure in
children undergoing UCBT {[}6, 7{]}. During the initial months following
HSCT, T cell reconstitution is dependent on homeostatic peripheral
expansion of graft T cells. \emph{In-vivo} graft T cell depletion by ATG
adversely impacts homeostatic peripheral expansion. Thymopoiesis is
established around 4-6 months post-HSCT and subsequently contributes to
T cell reconstitution. In our patient, T cell recovery along with
presence of RTE was noted at 5 months post-UCBT, which is consistent
with recovery through thymopoiesis. Based on our experience, it may be
prudent to consider a lower dose or earlier administration of rATG in
the setting of UCBT for SCID to deplete host rather than non-primed cord
blood T and NK cells.

One of the advantages of using UCB in the treatment was higher
likelihood of B cell engraftment and decreased need for long term IVIG
{[}9{]} {[}3{]}, also in contrast to T cell depleted haploidentical and
matched unrelated bone marrow transplants {[}10{]} {[}11{]}. Other
advantage of using UCBT in SCID is lower risk of transmitting infections
and viral reactivation following engraftment {[}12{]}, which has been a
problem with unrelated donor or TCR\selectlanguage{greek}αβ-\selectlanguage{english}depleted haploidentical HSCT as
well as with alemtuzumab conditioning {[}3, 5, 13{]}.

In a T cell--depleted graft, circulating T cells may not be detected for
several months after transplantation {[}14{]}; which might increase the
risk of infection. However, our patient did relatively well with
anti-microbial prophylaxis. As reported previously, T cell-depleted UCBT
may have a superior B cell engraftment in IL-7R\selectlanguage{greek}α-\selectlanguage{english}mutated SCID {[}9{]}
paralleling our experience as mixed chimerism was observed in the B-cell
lineage along with normal serum immunoglobulin levels without
supplementation. In conclusion, UCBT with modified ATG conditioning can
be an acceptable alternative in IL-7R\selectlanguage{greek}α-\selectlanguage{english}mutated SCID cases when
HLA-matched sibling donor or newly advanced graft T cell depletion
strategies are not available {[}6, 7{]}.

\textbf{Statements and Declarations}

\textbf{Funding}

The authors declare that no funds, grants, or other support were
received during the preparation of this manuscript.

\textbf{Competing Interests}

The authors have no relevant financial or non-financial interests to
disclose.

\textbf{Author Contributions}

The first draft of the manuscript was written by Eman Al-Antary and
S\selectlanguage{ngerman}üreyya Sava\selectlanguage{polish}ş\selectlanguage{english}an and all authors commented on previous versions of the
manuscript. All authors read and approved the final manuscript.

\textbf{Data Availability}

The patient data summarized in the current report are available from the
corresponding author on reasonable request.

\textbf{Ethics approval}

This is a brief report summarizing patient's clinical course. The
Children's Hospital of Michigan Research Ethics Committee has confirmed
that no ethical approval is required.

\textbf{Consent to publish}

The authors affirm that parents of our reported patient provided
informed consent for publication.

\textbf{References}

1. Buckley RH. Molecular defects in human severe combined
immunodeficiency and approaches to immune reconstitution. Annual review
of immunology. 2004;22:625-55.

2. Fernandes JF, Rocha V, Labopin M, Neven B, Moshous D, Gennery AR, et
al. Transplantation in patients with SCID: mismatched related stem cells
or unrelated cord blood? Blood. 2012;119(12):2949-55.

3. Tsilifis C, Lum SH, Nademi Z, Hambleton S, Flood TJ, Williams EJ, et
al. TCR\selectlanguage{greek}αβ-\selectlanguage{english}Depleted Haploidentical Grafts Are a Safe Alternative to
HLA-Matched Unrelated Donor Stem Cell Transplants for Infants with
Severe Combined Immunodeficiency. Journal of clinical immunology. 2022.

4. Haddad E, Leroy S, Buckley RH. B-cell reconstitution for SCID: should
a conditioning regimen be used in SCID treatment? The Journal of allergy
and clinical immunology. 2013;131(4):994-1000.

5. Dvorak CC, Patel K, Puck JM, Wahlstrom J, Dorsey MJ, Adams R, et al.
Unconditioned unrelated donor bone marrow transplantation for IL7R\selectlanguage{greek}α- \selectlanguage{english}and
Artemis-deficient SCID. Bone marrow transplantation. 2017;52(7):1036-8.

6. Admiraal R, Boelens JJ. Anti-thymocyte globulin for GVHD: one dose
does not fit all. The Lancet Haematology. 2020;7(7):e505.

7. Admiraal R, Boelens JJ. Pharmacotherapy in Pediatric Hematopoietic
Cell Transplantation. Handbook of experimental pharmacology.
2020;261:471-89.

8. Admiraal R, Lindemans CA, van Kesteren C, Bierings MB, Versluijs AB,
Nierkens S, et al. Excellent T-cell reconstitution and survival depend
on low ATG exposure after pediatric cord blood transplantation. Blood.
2016;128(23):2734-41.

9. Chan WY, Roberts RL, Moore TB, Stiehm ER. Cord blood transplants for
SCID: better B-cell engraftment? Journal of pediatric
hematology/oncology. 2013;35(1):e14-8.

10. Buckley RH. B-cell function in severe combined immunodeficiency
after stem cell or gene therapy: a review. The Journal of allergy and
clinical immunology. 2010;125(4):790-7.

11. Grunebaum E, Roifman CM. Bone marrow transplantation using
HLA-matched unrelated donors for patients suffering from severe combined
immunodeficiency. Immunology and allergy clinics of North America.
2010;30(1):63-73.

12. Gluckman E, Rocha V, Chevret S. Results of unrelated umbilical cord
blood hematopoietic stem cell transplant. Transfusion clinique et
biologique : journal de la Societe francaise de transfusion sanguine.
2001;8(3):146-54.

13. Lane JP, Evans PT, Nademi Z, Barge D, Jackson A, Hambleton S, et al.
Low-dose serotherapy improves early immune reconstitution after cord
blood transplantation for primary immunodeficiencies. Biology of blood
and marrow transplantation : journal of the American Society for Blood
and Marrow Transplantation. 2014;20(2):243-9.

14. Haddad E, Landais P, Friedrich W, Gerritsen B, Cavazzana-Calvo M,
Morgan G, et al. Long-term immune reconstitution and outcome after
HLA-nonidentical T-cell-depleted bone marrow transplantation for severe
combined immunodeficiency: a European retrospective study of 116
patients. Blood. 1998;91(10):3646-53.

\textbf{Figure Legend}

Figure 1. Immune reconstitution following umbilical cord blood
transplantation (UCBT). \textbf{A} . Time frame of immune recovery is
depicted in this illustration. TREC (T cell receptor excision circles)
presented in cells/mcL; STR (short tandem repeat) in percent values; PHA
(Phytohemagglutinin); PWM (Pokeweed); Con A (Concanavalin A).\textbf{B}
. Post-UCBT immune reconstitution course of T cells (CD3+), recent
thymic emigrants (RTE) that are CD3+CD4+CD45RA+CD31+, CD5-dim T cells,
CD4+ T cells and CD8+ T cells in percent values of the denominator
population. Higher CD5-dim T cell ratios in earlier days of immune
reconstitution may reflect greater release of maturing thymocytes into
circulation. \textbf{C} . Flow cytometry histograms reflecting the
pattern of CD3+/CD4+ cells, RTE, CD56+/CD16+/-- cells and CD5-dim T
cells (all gated on lymphocyte population) 10 months following UCBT.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/SCID-Figure-1-A-B-C/SCID-Figure-1-A-B-C}

\end{center}
\end{figure}

\textbf{Hosted file}

\verb`Delayed T cell Reconstitution Following UCBT Conditioned with Thymoglobulin in IL7R-SCID-BMT-Figure1.pptx`  available at \url{https://authorea.com/users/512098/articles/588708-delayed-but-successful-t-cell-immune-reconstitution-following-umbilical-cord-blood-transplantation-conditioned-with-thymoglobulin-alone-in-il-7r%CE%B1-mutated-scid}

\selectlanguage{english}
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