Method for determining the amount of a therapeutic antibody in the brain

1. A method for determining the concentration of a therapeutic antibody in a tissue of an experimental animal, whereby the tissue has a barrier to the blood circulation of said animal and whereby the therapeutic antibody had been administered to said experimental animal, wherein the interference from residual blood in a tissue sample of the experimental animal, which is used for determining the concentration of the therapeutic antibody in said tissue, is reduced, the method comprising the following steps of administering a therapeutic antibody and an inert reference antibody to the experimental animal,

i) determining the concentration of the therapeutic antibody in a blood sample of the experimental animal,

ii) determining the concentration of the therapeutic antibody in the tissue sample of the experimental animal,

iii) determining the concentration of an inert reference antibody in the blood sample of the experimental animal,

iv) determining the concentration of the inert reference antibody in the tissue sample of the experimental animal,

v) determining the tissue concentration in the tissue sample,

and determining the concentration of the therapeutic antibody in the tissue of the experimental animal with the following formula:

C

tmAb

,

tissue

=

C

tmAb

,

tissue

,

det

.

C

tissue

,

sample

-

C

refmAb

,

tissue

,

det

.

C

tissue

,

sample

C

refmAb

,

plasma

.

det

.

*

C

tmAb

,

plasma

,

det

.

with

C tmAb,plasma,det. =concentration of the therapeutic antibody of i)

C tmAb,tissue,det. =concentration of the therapeutic antibody of ii)

C refmAb,tissue,det. =concentration of the inert reference antibody of iii)

C refmAb,plasma,det. =concentration of the inert reference antibody of iv)

C tissue,sample =tissue concentration of v)

whereby the inert reference antibody does not cross said barrier between the tissue and the blood circulation,

whereby the inert reference antibody had been administered i) either together with the therapeutic antibody in case the sample is to be taken within 5 minutes after the administration of the therapeutic antibody, or ii) 2 to 10 minutes prior to taking the tissue sample,

whereby the blood sample is taken directly prior to the tissue sample, wherein the inert reference antibody is DP47GS, wherein the inert reference antibody comprises a heavy chain variable region and a light chain variable region, wherein the heavy chain variable region comprises the amino acid sequence of SEQ ID NO: 67 and the light chain variable region comprises the amino acid sequence of SEQ ID NO: 68.

2. The method according to claim 1 , wherein the tissue is either brain tissue and the therapeutic antibody can cross the blood-brain-barrier or ocular tissue and the therapeutic antibody can cross the blood-ocular-barrier.

3. The method according to claim 1 , wherein the therapeutic antibody is a bispecific antibody.

4. The method according to claim 1 , wherein the therapeutic antibody is specifically binding to human transferrin receptor and a brain target.

5. The method according to claim 4 , wherein the brain target is selected from the group consisting of human CD20, human Abeta, human alpha-synuclein, human tau, human glucocerebrosidase, human lingo-1, and human huntingtin.

6. The method according to claim 1 , wherein the experimental animal is selected from mouse, rat, rabbit, dog, sheep, ape, and monkey.

7. The method according to claim 1 , wherein the experimental animal is a non-human experimental animal with a body weight of more than 100 g and less than 15 kg.

8. The method according to claim 1 , wherein the experimental animal is a cynomolgus monkey.

9. The method according to claim 1 , wherein the inert reference antibody is a human germline antibody.

10. The method according to claim 1 , wherein the inert reference antibody does not cross said barrier in detectable amounts within 15 minutes after its application.

11. The method according to claim 10 , wherein the inert reference antibody does not cross said barrier in detectable amounts within 10 minutes after its application.

12. The method according to claim 1 , wherein the inert antibody is administered about 5 minutes prior to taking the tissue sample.

13. The method according to claim 1 , wherein the tissue is perfused with an aqueous solution directly after taking the blood sample and prior to taking the tissue sample.

14. The method according to claim 1 , wherein the determining of the concentrations is by a bridging ELISA.