Non-clinical package
In total 218 ATMP advice reports from 2013 until 2018 were collected
from the EMA database, containing information on 153 different products.
Of these, 59 were gene therapy medicinal products (GTMPs) not consisting
of cells, which were excluded from the study. One product was excluded
from the database, because it contained xenogeneic cells and seven
products were excluded, because information on the non-clinical program
was lacking. The remaining 86 products were categorized based on cell
origin and on genetic modification status (Figure 1). The majority of
cell therapies in development for which advice was requested during the
2013-2018 period, were not genetically modified (n= 60, 70%). Of
these,31 were of autologous origin and 29 were of allogenic origin. The
majority of the genetically modified cells were autologous of origin
(n=20, 23%) and only six (7%) products were genetically modified,
allogenic cells.
In total 234 in vivo studies were performed for 80 of the 86
products, and for some products additional animal studies were
envisaged. The six products for which in vivo animal studies were
not conducted, planned or requested did not contain genetically modified
cells (data not shown). Pharmacology, which mainly accounts for
proof-of-concept (PoC), was studied for most of the products, followed
by safety (Figure 2). The number of products with biodistribution and
tumourigenicity animal studies was slightly lower. For these types of
studies information on biodistribution (8 products) and tumourigenicity
(14 products) was not always present in the non-clinical data package
provided by the sponsor. It is not known whether sponsors did not regard
studies addressing biodistribution and tumourigenicity of value for
their product or whether the product was not yet in the stage of
development that the issue of biodistribution and/or tumourigenicity
study would be relevant to address.
In guidelines for ATMPs it is recommended to combine the various
endpoints addressing e.g. pharmacology and safety in one study if
possible and sensible, resulting into a so-called combination study
[7]. Across the different types of in vivo studies,
pharmacology was most often evaluated in dedicated studies, whereas
safety was often studied in combination studies (Figure 3).
Biodistribution
For at least half of the products the sponsor regarded an in vivoanimal study of value for the evaluation of the biodistribution of their
product, as for 49 of 86 products (57%) a biodistribution study was
either conducted (n=40; 47%) or planned (n=9; 10%) (Table 1). For 25
products, the non-clinical data package contained two or more in
vivo biodistribution studies. For the products (n=37; 43%) for which a
biodistribution study was not conducted nor planned, this was agreed
upon by the regulators either immediately (n=21) or when supported by
further justification (n=3). For five products (6%) the regulators
requested a biodistribution study in animals. For eight products (9%),
a discussion on the biodistribution was lacking in the sponsor’s
documentation and was not discussed by the regulators in the advice
report. Thus, for 24 of 86 products (28%), both sponsors and regulators
considered there was no need for in vivo studies on
biodistribution. There were no large differences in the presence or
absence of in vivo biodistribution studies between the product
categories (Table 1). Even though for most products biodistribution was
studied in a dedicated study (30 of 49 products), sponsors indicated
that the results were of value for both understanding the PoC of their
product and its safety profile. For several products the value of the
biodistribution study for PoC-only or for safety-only was recognized
(respectively n=4 and n=11).
For nine products biodistribution was studied in healthy and for twelve
products biodistribution was studied in diseased animals. For nine of
these it was explicitly noted that the model was homologous. For three
products no information was present on the model and for the remaining
25 products immunocompromised animals, reflecting heterologous models,
were used. For 42 products information on the method to evaluate
biodistribution was provided. The most commonly used techniques were
IHC, quantitative-PCR (qPCR) or reverse-transcriptase PCR (RT-PCR),
Fluorescence In Situ Hybridization (FISH), and microscopy. For
all these techniques tissue samples need to be harvested to allow for
detection of the cells. The more sophisticated techniques for studying
cell-distribution in vivo (such as Positron emission tomography
(PET), Single photon emission computed tomography (SPECT), Magnetic
resonance imaging (MRI) and Bioluminescence imaging (BLI)) were only
used to study biodistribution for three products.
The vast majority of biodistribution studies provided information on the
presence of the administered cells in/migration to both target and
non-target tissues (40/49; 82% of the products with biodistribution
studies, Figure 4). Only for four (autologous cell) products, sponsors
considered the option of assessing target tissue only (8% of the
studies). For five products it was not mentioned which tissues were
assessed (10%). Information on the relative distribution of the
administered cells was available for 42 (86%) of the 49 studies,
suggesting that the method to determine biodistribution of the
therapeutic cells was also (semi-)quantitative.
Information on persistence of the administered cells was available for
44 products (51%). For another 10 products (12%) sponsors planned to
evaluate in vivo persistence in the future, whereas for 13
products (15%) sponsors did not aim to address it (Figure 5). For the
remaining 19 products there was nothing mentioned regarding persistence
in the submitted information.
Tumourigenicity
Remarkably, while FDA guidance [11] specifically stipulates that for
tumourigenicity studies the intended clinical product should be used
(and not analogous animal cells), tumourigenicity was studied in a
homologous model for eight products of which three were studied in
healthy and five in diseased animals. For one product it was not
mentioned and for remaining 37 products immunocompromised animals,
reflecting heterologous models, were used. The chosen route of
administration (RoA) was most often intravenous or subcutaneous and
mainly a dose of 1x106 cells was applied (Table 2).
For two products, various doses were used and for ten products the
administered dose in the study was not mentioned (most often for planned
studies). While there was some variability in the duration of thein vivo tumourigenicity studies, a study duration between three
and six months was noted for the majority of the products (n=28 of 46).
For most products the tumourigenic potential was addressed by
experimental data (in vitro and/or in vivo studies), only
for 10 products (11%) sponsors did not investigate the tumourigenic
risk with any experimental data. Of note, for 14 (16%) products there
was no information on tumourigenicity studies in the documentation. For
nine products (10%), the risk for tumourigenicity was investigated byin vivo studies only, for 18 products (20%) the tumourigenic
risk was only evaluated by in vitro assays, and for 37 products
(43%) both in vivo and in vitro studies were used to
address this potential risk (Figure 6). Thus for 46 of the 86 products
in the database tumourigenicity was studied and/or planned to be studiedin vivo (Figure 2). For 18 of the 46 products with in vivotumourigenicity studies, more than two in vivo studies
tumourigenicity studies were part of the development package. This often
concerned the combination of a dose range finding study and a pivotal
study, or the assessment of tumourigenic risk upon various routes of
administration.
For 16 of the 40 products for which no in vivo study was
performed or planned, it was explicitly agreed that an in vivostudy was not necessary, while for six products regulators indicated
that the absence of in vivo studies could be acceptable provided
that the company justified the absence of such a study. This was
apparently most often the case for the genetically modified products
(Table 3). For four products an in vivo animal study was
explicitly requested. Products for which tumourigenicity was studied
with only in vitro studies most often contained genetically
modified cells (Figure 6). For products containing allogeneic
genetically modified products, tumourigenicity was always discussed
The in vitro tumourigenicity studies in the 55 (64%) products
most often consisted of karyotyping (n=28) and/or colony
formation/proliferation assays (n=22). For 22 products, multiple types
of in vitro studies were performed (Table
4).