Dear All,Back to the Top
We are currently evaluating the pharmacokinetics of a murine/human
chimeric monoclonal antibody following three 60 mg/kg infusions
(separated by a 1-week interval) in premature neonates.
Blood was collected 1-3 hours, 3 and 7 (i.e before next infusion) days
after each infusion and additionally 14 and 28 days after the last
infusion. The mAb concentration was then determined in serum by ELISA.
In several occasions, we observed a plateau (low concentration decrease
or sometimes even a slight re-increase) in the concentration-time
profile between 3 and 7 days after infusion.
Here are the data of one subject with this kind of behaviour:
[ 1st infusion ]
7.0104 239 (2 ug/mL decrease)
[ 2nd infusion ]
14.0368 362 (3 ug/mL re-increase)
[ 3rd infusion ]
20.9965 561 (50 ug/mL re-increase)
I am not really familiar with the pharmacokinetics of antibodies and I
do not find any similar result after a quick search in the litterature.
Does anyone have any experience or relevant explanation, or has this
already been described elsewhere?
Many thanks in advance for your help.
SGS Biopharma - Wavre - Belgium
Dear Fabrice,Back to the Top
The measurement of monoclonal antibodies in serum by ELISA poses a
number of assay issues that likely account for your results.
The ELISA is likely not as quantitatively accurate as analytical assays
for an NCE and highly dependent on the assay conditions. Hence, if you
run the ELISA assay in multiple wells, you will come up with slightly
different concentrations and depending on the dilution factor, this may
be the reason for slight differences in concentrations on different
Depending on the type of ELISA used, different dilution factors for the
serum can give quite different concentration values. If you have an
ELISA that is able to measure total antibody, both bound and unbound,
then dilution becomes less problematic. However, if the ELISA is only
able to measure antibody in the serum that has one or both arms free
(depending on the ELISA), then such an ELISA is prone to the change in
the equilibrium between bound and free antibody that occurs with serum
sample dilution. If your ELISA is measuring only free antibody in the
serum (the capture and detection antibodies in the ELISA are the same),
then dilution of the serum sample will result in some dissociation of
your antibody of interest from its antigen and a higher "apparent"
concentration of free antibody of interest in your serum sample.
Another explanation may be that the chimeric antibody is generating an
anti-antibody response. Such a response would also affect your
quantitation of antibody in the serum. Depending on the ELISA used, an
anti-antibody response could produce a false higher or lower
I hope this helps a little. Perhaps if you provided more detail
regarding the ELISA.
Jeffrey L. Larson, Ph.D.
Director of Toxicology and Pharmacokinetics
10555 Stella Link
Houston, TX 77025
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