Dialyzable leukocyte extracts (DLE) are heterogeneous mixtures of peptides under 10 kDa, released after disruption of peripheral blood leukocytes from healthy donors [1] . It has been reported that administration of DLE improves clinical responses in allergies [2] , in infections and immunodeficiency syndromes [3] - [5] , and in some other immune-mediated diseases (reviewed in [6] ). The therapeutic adjuvant effect of DLE is associated with their ability to modulate immune responses changing innate signaling pathways, such as TLRs [7] , NF-kB, and cyclic adenosine monophosphate (cAMP) in cultured cells [8] [9] ; DLE could modulate production of cytokines, including TNF-a, IL-6 [10] [11] , and induce IFN-g secretion, driving immune response to a Th1 immune-regu- latory response [12] [13] .

Transferon^TM is a human dialyzable leukocyte extract manufactured by National Polytechnic Institute (IPN), Mexico, at Good Manufacturing Practice (GMP) facilities. Transferon^TM is registered by Mexican health authorities as a drug and is commercialized nationally. Although Transferon^TM is a mixture of peptides, it has been demonstrated that there is a high batch-to-batch reproducibility in the chromatographic profile and also in the biological efficacy, demonstrated in vitro by up-regulation of IFN-g in a lymphocytic cell line (Jurkat clone E6-1) [1] .

DLEs have been widely used since the 1970s due to their immune-regulatory functions for various clinical purposes [6] [14] [15] ; to date, there are no current reports about the safety of Transferon^TM; thus, it was the aim of our study.

Dialyzable leukocyte extracts are heterogeneous mixtures of polar and hydrophilic peptides under 10 kDa, released after disruption of peripheral blood leukocytes from healthy donors [1] . DLE have been used to modulate immune response [1] [10] - [13] in patients suffering immune-mediated diseases [6] [14] [15] . Transferon^TM is a human dialyzable leukocyte extract manufactured by National Polytechnic Institute (IPN), Mexico, at GMP facilities. The use of Transferon^TM is widely extended in our country [6] ; but despite their broad clinical use, to our knowledge no adverse events have been studied before.

In this work, we observed a low frequency of AE with the use of DLE. A significant adverse effect is usually considered as a reaction present in at least 2% of the studied population [19] . Of all included patients, only 1.9% of them developed adverse events. These results suggest that DLE is a safe and tolerable substance, but the unexpected low incidence of adverse events also opens the possibility of Transferon^TM-related adverse events may remain under-diagnosed.

Comparing our adverse event profile with adverse effects of glatiramer acetate (GA), a four peptide-based product with 5 - 9 kDa in size [19] - [21] , we did not find similarities. GA is an injectable synthetic amino acid- based product with immune regulatory properties, reported incidence of adverse effects is at least 10%, mostly related to injection-site reaction. DLE is an oral peptide mixture lower than 10 kDa in size, and even though oral and injectable formulations cannot be fully compared, we expected to find some similar adverse effects between Transferon^TM and GA. Nevertheless, some interesting patterns in adverse events presentation with the use of

Transferon^TM are worth analyzing, i.e. AE were more frequent in females, and we detected 2 vulnerable age groups: ages 1 to 10, and 40 - 60 years old; this suggests that dosing should be reevaluated in order to reduce adverse events in both groups, and physicians need to increase clinical supervision to opportunely detect AE in children. It is unknown if hormonal factors may be involved in the female predominant adverse event profile showed in our study, but it is recognized that hormones may influence drug metabolism. Gender differences in adverse drug events have been observed before [22] [23] , and factors other than hormonal effects such as body weight and differences in pharmacokinetics may be involved. In order to determine if hormonal factors are related in this pattern, it would be desirable to further study adverse event incidence in different female groups, such as before menarche and after menopause.

In this study we observed that most common AE were headache, followed by rash, increased disease-related symptomatology, rhinorrhea, cough and fatigue. In line with our results, the most common side effects of IFN- gamma include fever, chills, fatigue, myalgia, and headache [24] - [26] , and it is well known that Transferon^TM induces IFN-g in vivo [12] [13] , and in vitro [1] . On the other hand, some DLE have been associated to an in vitro transient elevation of cAMP [8] [9] , and increased concentrations of cAMP are related with headache [27] - [29] , rhinorrhea [30] [31] , and fatigue [32] - [34] . If Transferon^TM is able to increase cAMP it is unknown, and needs further investigation. Importantly, no serious AE were observed in this study.

The study population was heterogeneous, involving an extensive age group and patients presenting various different diseases as well as varied concomitant treatments for these diseases. Additional studies should be conducted in a controlled population. The low incidence of adverse events elevates the possibility that adverse events may be under-reported, and strengthening our pharmacovigilance protocols will aide in this matter. Finally, the lack of other adverse reaction reports associated to human DLE limits our possibility of comparison.

To our knowledge, no data on the adverse event profile of other DLEs have been published, and this study is an adequate first step to describe adverse events associated with DLE and Transferon^TM; Transferon^TM induced low frequency of nonserious adverse events during adjuvant treatment; however, further monitoring is advisable for different age and disease groups of patients.

S. E-P and M. P-T have been compensated for their work by UDIMEB, the producer of Transferon^TM. All other authors declare no conflict of interest.

T.H.―performed clinical evaluation, analyzed and interpreted clinical immunological data, and wrote the paper; V.S.―trained medical staff in pharmacovigilance and developed pharmacovigilance procedures according to Mexican regulation. V.S., J.G.-C.; I.L.―collected clinical information, and analyzed data; E.C.-T., M.C.A., E.V., O.P., J.A.-B.―performed clinical-immunological evaluation of patients; A.E-G.―analyzed data, wrote paper; S.E.-P.―contributed with critical criticism of paper and wrote paper; M.P.-T. and M.C.J.-M.―designed the study, analyzed data, wrote paper and conducted research. A.E.-G. received a PhD scholarship from CONACyT number 164000.