Pediatr Blood Cancer

HIGHLIGHTby Roberta H. Adams, MD

1,2*

Infectious Disease Testing for Cellular Therapy

M esenchymal stromal cells (MSC) are multipotent stem

cells which can be isolated from a wide range of human

tissue types, including bone marrow, adipose tissue, umbilical cord

cells, as well as more primitive cells such asWharton’s jelly stromal

cells [1,2]. These cells are capable of differentiating in vitro into a

variety of cell types (bone, cartilage, adipose tissue, tendon,

muscle) [3]. Because of their ability to differentiate into multiple

mature cell types, their unique lack of immunogenicity, and their

immunosuppressive and anti-inflammatory qualities, these cells are

being used extensively in experimental animal and human

conditions to address clinical challenges ranging from tissue repair

and regeneration to control of graft versus host disease. Many of the

patient populations being studied are immunocompromised, either

following an allogeneic stem cell or solid organ transplant or

because of underlying immune dysregulation. To date,>900 HSCT

patients have received MSC infusions for treatment of steroid

refractory acute GVHD. Short term follow up of these patients has

documented the safety of these cell products, and has failed to

demonstrate infectious or tumorigenic risks associated with the use

of these products. Publications have explored the risk of viral

infectivity of MSC’s and the subsequent transmission and infection

risk of herpes family of viruses [4,5] and Hepatitis. While MSC are

susceptible to in vitro infection, only limited viral gene expression

has been documented, leading to what appears to be a nonproduc-

tive infection.

In this issue of Pediatric Blood and Cancer, Comar et al. [6]

investigated the rate of detection of DNA from polyoma viruses

(JCV, SV40, BK, and Merkel cell [MCPyV]) in mesenchymal

stromal cells derived from human Wharton’s jelly matrix. They

studied 35 umbilical cord samples and were able to detect viral

DNA from JCV in 1/35 cord samples (2.8%) and from SV40 in 3/35

cord samples (8.6%). Viral copy numbers were very low but

detectable for both of these viruses (mean viral load 2.8� 10/

5� 103 beta globin reference gene sequences). Viral DNA was

undetectable for BK and MCPyV. The authors note the very low

viral copy number, but raise the concern ofMSC infection with viral

agents, especially those know to be tumorigenic. Despite the rare

rate of infection demonstrated in this study, the long term risk of in

vivo viral expansion and potential tumor development in this

immunocompromised patient population is appropriately raised

and should be further studied.

Currently, clinical release criteria for cellular therapy products

vary between countries, with no single comprehensive international

standard. Investigators must comply with country-specific regula-

tory bodies, as well as voluntarily comply with the international

organizations JACIE and FACT-netcord. Additionally, production

of cellular therapy products within the United States or shipped into

the US must comply with good manufacturing practices governed

by the Department of Health and Human Services Food and Drug

Administration (FDA). Generally, country-specific agencies re-

quire testing for the presence of a wide range of human bacterial,

fungal and viral infections, including CMV, HTLV-1 and -2, HIV-1

and -2, and the hepatitis viruses, both in the donor as well as the

manufactured cell product. Additional testing varies from country

to country, using a combination of NAT testing and serologic testing

for the infections noted above plus variable additional infectious

agents, depending on donor history. Although there is significant

uniformity between countries in testing and release requirements,

there remain differences and gaps because of the multitude of

country specific regulatory agencies [7].

There is much less uniformity or consistency in country

requirements for testing for rare or unknown infections. The FDA

mandates the use of adventitial agent testing using a range of in vitro

and in vivo animal models to identify rare or unknown infections,

including viral infections, prior to release of products that have

derived from transformed cell lines. This requirement, however, has

not applied to expanded but non-immortalized cell lines.

Polyoma viruses are well recognized to cause infection in the

CNS and genitourinary system of immunocompromised patients

and to have tumorigenic capability, especially in neuroectodermal

tissue. Fortunately this type of infection has not been reported in

association with cellular therapy.

As the cellular therapy community continues to improve and

refine safety monitoring, questions that must be kept at the forefront

when reviewing new regulatory testing include:

What is the risk/benefit ratio of the proposed test?

Does detection of trivial amounts of viral DNA equate to the

ability to cause infection?

Will more restrictive testing improve the safety of the product

or simply make access more difficult without improving

safety?

As the authors point out, it is critical to recognize the infectious

potential of human stromal cells and to develop international

consensus guidelines, including testing and detection of rare viruses

1Consultant, Hematology/Oncology, Dept of Internal Medicine, Mayo

Clinic Arizona, Phoenix, AZ; 2Director, Pediatric Blood and Marrow

Transplant, Phoenix Children’s Hospital, Phoenix, AZ

�Correspondence to: Roberta H. Adams, 5777 East Mayo Blvd,

Phoenix, Az 85054. E-mail: adams.roberta@mayo.edu

Received 10 March 2014; Accepted 10 March 2014

�C 2014 Wiley Periodicals, Inc.DOI 10.1002/pbc.25052Published online in Wiley Online Library(wileyonlinelibrary.com).

in these valuable cell products. It is incumbent on the medical and

scientific community to rigorously study and monitor this risk of

infectious transmission, using ever-evolving technologies to search

for evidence of cellular infection. World-wide minimal release

criteria must be established to continue to maintain the highest

standards of safety for cellular products. This is a challenging task

that is being tackled bymultiple groups, including among others the

World Health Organization, and a joint effort of an International

Forum between the ISBT-AABB Working Party of Cellular

Therapies. However, it is equally important to do this without

unnecessarily restricting patient access to this therapeutic option—

hematopoietic stem cells, mesenchymal stromal cells, dendritic cell

vaccines, and the increasing array of therapeutic cells developed

from a wide array of human tissue sources. The burgeoning field of

human cellular therapy is opening up vast new possibilities of

therapeutic intervention. It is incumbent upon the scientific

community to continue expansion of cell therapy while maintaining

vigilance to ensure that the products that are available remain safe,

both from short and long term complications.

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6. ComarM, Delbue S, Zanotta N, et al. In vivo detection of polyomaviruses JCVand SV40 in mesenchymal

stem cells from human umbilical cords. Pediatr Blood Cancer 2014; DOI: 10.1002/pbc.24943

7. Eichler H, Schrezenmeier H, Schallmoser K, et al. Donor selection and release criteria of cellular therapy

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Pediatr Blood Cancer DOI 10.1002/pbc

2 Adams