Pfizer v. Genentech
`IPR201(cid:26)-01488
`Genentech Exhibit 20(cid:21)(cid:19)
`
`

`

`4286
`
`Immunology: Carter et al.
`
`Proc. Natl. Acad. Sci. USA 89 (1992)
`
`muMAb4D5 VL
`40
`30
`20
`10
`D
`H
`D
`I V M T Q S
`P
`I T C K A S Q D V N T A V A W Y Q Q K
`R V S
`K F H S T S V G
`GCTGATATCGTGATGACCCAGTCCCACAAGTTCND3DJHKI3H7RFFiIXIaHAGGGTCAGCA1CAEIflYIIAGGCCAGTCAGGA1GTGAAHICDQfflFTNEJTRIFFATCAACAGAAACCA
`an n. n -
`GCTGATATCCAGATGACCCAGTIX1XJ3AGC1YIKID3flXX;JTFCFFF3GGCGA1AIKXFD2ACCATCAKI7H33I3F33GAG1C1GGA1V1D3AAflVKFD3IDETAGCKHVISFATCAACAGAAACCA
`D
`I Q M T Q S
`P
`S
`S
`L
`S A S V G
`D R V T I T C
`R A S 9 D V N T A V A W Y Q Q K
`P
`vL—-coru
`huMAMDS-S VL
`
`50
`Y S A S
`
`G H S
`
`F K L L
`
`G K A P
`
`K
`
`L L
`
`I
`
`I
`
`F R Y T G V
`
`P
`
`60
`D R
`
`5
`I
`F T G N R
`
`A
`S
`
`70
`G T D
`
`F T F T I
`
`Y
`
`F
`S A S
`vL—cuu
`
`L
`
`E S G V P
`
`S
`
`R
`
`F
`
`S
`
`G S
`
`R
`
`S G T D
`
`F T L T I
`
`A
`
`B
`
`80
`S V 0 A E
`
`S
`
`L Q
`
`P
`
`E
`
`S
`
`S
`
`FIG. 1. Nucleotide and amino
`acid sequences of mumAb4D5 and
`humAMDS-S V; (A) and VH (B)
`(numbered according to ref. 26).
`The CDR residues according to a
`sequence definition (26) and a
`structural definition (22) are un-
`derlined and overlined, respec-
`tively. The 5’ and 3’ ends of the
`oligonucleotides used for gene
`conversion mutagenesis are
`shown by arrows and mismatches
`between genes are shown by as-
`terisks. The asparagine-linked gly-
`cosylation site (#) in mumAb4D5
`VL is used in some mumAb4D5
`molecules derived from the corre-
`sponding hybridoma. However,
`mumAb4D5 variants, which are
`glycosylated or aglycosylated in
`VL, are indistinguishable in their
`binding affinity for the p18SHER2
`ECD and in their antiproliferative
`activity with SK-BR-3 cells (C.K. ,
`M. Spellman, and B. Hutchins,
`unpublished data).
`
`100
`90
`K
`I
`P T F G G G T K V E
`P
`D L A V Y Y C Q Q H Y T T
`GAKIIn332AG111A1TACflYFD2AGCAACAT1ATIEfl2KflEIflLXX3KIFFDI1EU3331FTACCAAGGTGGAGATCAAA
`GACTFJXIAIH1A11ACTGTCAGCAACNTTATACTAEflKXfltXImCGT1CGGACAGGGTACCAAGGTGGAGATCAAA
`D F A T Y Y C Q 9 H Y T T P
`P T F
`G Q G T
`K V E
`I
`K
`VL-CDRB
`
`30
`20
`10
`muMAMDS VH
`H W V K
`I
`K D T Y
`C T A S G F N I
`S
`G A S
`L V K P
`P
`L K L
`E
`Q V 0 L Q Q S G
`an
`an
`GJEHKXXflCN1H1CAGCDI1GCN3R3flIIXXflGAGCDIflGANIKIGGGI37N3MflIJAGTflFflXflGTACN3ETDTKIXHHCAACNPTAAAGACNJH“HATACACEIXHGAAA
`GaETACXi3D3AIXFFF:AGIflVXFRIflKIDIDIIJ3SRIiJ3HIFn33UI32ALKIIII3ICAEflVXIFPFn3DI3flFDI3VRTFD3FI33FF2AACAH1AAAGACAKIHTHITTCACHTXIFHEJEF
`E V Q L V B
`S G G G L V Q P G G S
`L
`R L
`S
`C A A S G F N I
`K D T Y
`I
`H W V R
`vH-coru
`
`huMAMDS-S VH
`60
`40
`a
`50
`7°
`S N T A
`P K F O D K A T I T A D T S
`Y D
`Y
`Q R
`P
`E Q G L
`P T N G Y T R
`E W I G R I
`1V3AKXII3AAKFETISIAKIEACAAEXIIIAKTPA
`TAACAGCAGACACATCKHEIZACACAGCC
`CN3I1XHGGAAJGGNPRIHAGGATTTAflJflTCEANDIHHEflACflAGATA
`a .«n «an
`e
`a tt‘t'
`non
`« ttt
`CAGGCKXXXIIIPAAIXXII2F33AAflKIIFPnI2AAGGAT1111IIflWKl3AA1VIFFTAHACTAGATAflIXXJ3ATAtKIFF2AAKXII333FTF2ACTATAAKIJJCAGACACATCCAAAAACACAGCC
`T N G Y T R
`Q A P
`G
`K G L
`E W V A R
`I
`Y P
`Y A D S V K G R
`F T I
`S A D T S
`K N T A
`vH—cuzz
`
`110
`100 a
`90
`c
`b
`a
`80
`S
`R W G G D G F
`Y A H D Y W G Q G A S V T V S
`Y C S
`E D T A V Y
`L T S
`R
`Y L O V S
`tit.
`at. t a
`TNI3GCNRFn3MXXIXXflGACNFTDHMIaCACMEKIHYflATTATn1FKflMGNFfl3XflCGGGNUiXfl1CTNRIflTSGGACTICTEIXHVEAGGMIIICGGTCNJIFRJVXHEB
`1ACIflVI2AGATGAACAGCCflVKI3NI3F3AGGACACflYIIJSFIPA1TAfl1VFFN2IAGA1YXIaBU1133AI1XIIFR3TATViTTNn33AIXFDSDI3IFD2AAGGAALXXHYXFDDNJJSFZDJTFJS
`V W G O G T L V T V S
`S
`Y L Q N N S
`L
`R A E D T A V Y
`Y C S
`R W G G D G F Y A M D
`Vg<w
`
`dues (25, 26) incorporating restriction sites for directional
`cloning shown by underlining and listed after the sequences:
`VL sense, 5'~TCCGATATCCAGCTGACCCAGTCTCCA-3’
`EcoRV; VL antisense, 5’-GTTTGATCTCCAGCTT&
`TACCHSCDCCGAA-3’ Asp718; VH sense, 5’-AGGTSM-
`ARCTGCAGSAGTCWGG-3’ Pst 1; Va antisense, 5 ’-
`TGAGGAGACGGTGACCGTGGTCCC’I‘TGGCCCCAG-3’
`BstEII; where H is A, C, or T; S is C or G; D is A, G, or T;
`MisAorC; Ris AorG;WisAorT. The PCR products were
`cloned into pUC119 (27) and five clones for each V domain
`were sequenced by the dideoxynucleotide chain-termination
`method (28).
`Molecular Modeling. Models of mumAb4D5 VH and VL
`domains were constructed by using seven Fab crystal struc-
`tures from the Brookhaven Protein Data Bank (entries 2FB4,
`2RHE, 2MCP, 3FAB, 1FBJ, 2HFL, and 1REI) (29). VH and
`VL of each structure were superimposed on 2FB4 by using
`main-chain atom coordinates (INSIGHT program, Biosym
`Technologies, San Diego). The distances from each 2FB4 Caz
`to the analogous Ca1n each of the superimposed structures
`was calculated. For residues with all Ca—Ca distances<_1A,
`the average coordinates for individual N, Ca, C, O, and C3
`atoms were calculated and then corrected for resultant de-
`viations from standard bond geometry by 50 cycles of energy
`minimization (DISCOVER program, Biosym Technologies) us-
`ing the AMBER forcefield (30) and fixed Ca atoms. Side chains
`of FR residues were then incorporated, followed by inclusion
`of five of the six CDR loops (except VH—CDR3) using
`tabulations of CDR conformations (23) as a guide. Side-chain
`conformations were chosen on the basis of Fab crystal
`structures, rotamer libraries (31), and packing consider-
`ations. Three possible conformations of VH—CDR3 were
`taken from a search of similar sized loops in the Brookhaven
`Protein Data Bank or were modeled by using packing and
`solvent exposure considerations. Models were then sub-
`jected to 5000 cycles of energy minimization.
`A model of the humAb4D5 was generated by using consen-
`sus sequences derived from the most abundant human sub-
`classes—namely, VL K subgroup I and VH subgroup III (26).
`The six CDRs were transferred from the mumAb4D5 model
`onto a human Fab model. All humAb4D5 variants contain
`
`human replacements of mumAb4D5 residues at three positions
`within CDRs as defined by sequence variability (26) but not as
`defined by structural variability (22): VL—CDRI K24R, VL—
`CDR2 R54L and VL—CDRZ T56S.ll Differences between
`mumAb4D5 and the human consensus FR residues (Fig. 1)
`were individually modeled to investigate their possible influ-
`ence on CDR conformation and/or binding to p185HERZ ECD.
`Construction of Chimeric Gem. Genes encoding the chi-
`meric mAb4D5 light and heavy chains were separately as-
`sembled in previously described phagemid vectors contain-
`ing the human cytomegalovirus enhancer and promoter, a 5'
`intron, and simian virus 40 polyadenylylation signal (32).
`Briefly, gene segments encoding mumAb4D5 VL (Fig. 1A)
`and REI human K1 light-chain CL (33) were precisely joined
`as were genes for mumAb4D5 V" (Fig. IB) and human IgGl
`C region (34) by subcloning (35) and site-directed mutagen—
`esis as described (36). The IgGl isotype was chosen, as it is
`the preferred human isotype for supporting ADCC and CDC
`by using matched sets of chimeric (15) or humanized anti-
`bodies (17). The PCR-generated VL and VH fragments (Fig.
`1) were subsequently mutagenized so that they faithfully
`represent the sequence of mumAb4D5 determined at the
`protein level: VH, QlE; VL, V104L and T109A. The human
`IgGl C regions are identical to those reported (37) except for
`the mutations E359D and M361L (Eu numbering; ref. 26),
`which we installed to convert the antibody from the naturally
`rare A allotype to the much more common non-A allotype
`(26). This was an attempt to reduce the risk of anti-allotype
`antibodies interfering with therapy.
`Construction of Humanized Gem. Genes encoding chi-
`meric mAb4D5 light-chain and heavy-chain Fd fragment (VH
`and CHI domains) were subcloned together into pUC119 (27)
`to create pAKl and were simultaneously humanized in a
`single step (43). Briefly, sets of six contiguous oligonucleo-
`tides were designed to humanize VH and VL (Fig. 1). These
`oligonucleotides are 28—83 nucleotides long, contain 0—19
`mismatches to the murine antibody template, and are con-
`
`1Variants are denoted by the amino acid residue and number
`followed by the replacement amino acid.
`
`

`

`Immunology: Carter et al.
`
`Proc. Natl. Acad. Sci. USA 89 (1992)
`
`4287
`
`strained to have 8 or 9 perfectly matched residues at each end
`to promote efficient annealing and ligation of adjacent oligo-
`nucleotides. The sets of VH and VL humanization oligonu-
`cleotides (5 pmol each) were phosphorylated with either ATP
`or [7-32P]ATP (36) and separately annealed with 3.7 pmol of
`pAKl template in 40 pl of 10 mM Tris-HCl (pH 8.0) and 10
`mM MgCl2 by cooling from 100°C to =20°C over ~20 min.
`The annealed oligonucleotides were joined by incubation
`with T4 DNA ligase (12 units; New England Biolabs) in the
`presence of 2 p.1 of 5 mM ATP and 2 pl of 0.1 M dithiothreitol
`for 10 min at 14°C. After electrophoresis on a 6% acrylamide
`sequencing gel, the assembled oligonucleotides were located
`by autoradiography and recovered by electroelution. The
`assembled oligonucleotides (~03 pmol each) were simulta-
`neously annealed to 0.15 pmol of single-stranded deoxyuri-
`dine-containing pAKl prepared as described (38) in 10 pl of
`40 mM Tris-HCl (pH 7.5) and 16 mM Mng as described
`above. Heteroduplex DNA was constructed by extending the
`primers with T7 DNA polymerase and transformed into
`Escherichia coli BMH 71-18 mutL as described (36). The
`resultant phagemid DNA pool was enriched first for human
`VL by restriction purification using Xho I and then for human
`VH by restriction selection using Stu I as described (36, 39).
`Resultant clones containing both human VL and human VH
`genes were identified by nucleotide sequencing (28) and
`designated pAK2. Additional humanized variants were gen-
`erated by site-directed mutagenesis (36). The mumAb4D5 VL
`and V" gene segments in the transient expression vectors
`described above were then precisely replaced with their
`humanized versions.
`Expression and Purification of mAMDS Variants. Appro-
`priate mAb4D5 light- and heavy-chain cDNA expression
`vectors were cotransfected into adenovirus-transformed hu-
`man embryonic kidney cell line 293 by a high-efficiency
`procedure (32). Media were harvested daily for up to 5 days
`and the cells were refed with serum-free medium. Antibodies
`were recovered from the media and affinity purified on
`protein A-Sepharose CL-4B (Pharmacia) as described by the
`manufacturer. The eluted antibody was buffer-exchanged
`into phosphate-buffered saline by 025 gel filtration, concen-
`trated by ultrafiltration (Amicon), sterile-filtered, and stored
`at 4°C. The concentration of antibody was determined by
`both total IgG and antigen binding ELISAs. The standard
`used was humAb4D5-5, whose concentration had been de-
`termined by amino acid composition analysis.
`Cell Proliferation Assay. The effect of mAb4D5 variants on
`proliferation of the human mammary adenocarcinoma cell
`line SK-BR-3 was investigated as described (6) by using
`saturating mAb4D5 concentrations.
`
`Affinity Measurements. mAb4D5 variant antibodies and
`p18SHER2 ECD were prepared as described (40) and incubated
`in solution until equilibrium was found to be reached. The
`concentration of free antibody was then determined by
`ELISA using immobilized p185HER2 ECD and was used to
`calculate affinity (Kd) as described (41). The solution-phase
`equilibrium between p185HERZ ECD and mAb4D5 variants
`was found not to be grossly perturbed during the immobilized
`ECD ELISA measurement of free antibody.
`
`RESULTS
`
`Humanization of mumAb4D5. The mumAb4D5 VL and VH
`gene segments were first cloned by PCR and sequenced (Fig. 1).
`The V region genes were then simultaneously humanized by
`gene conversion mutagenesis using preassembled oligonucleo-
`tides. A 311-mer oligonucleotide containing 39 mismatches to
`the template directed 24 simultaneous amino acid changes
`required to humanize mumAb4D5 VL. Humanization of
`mumAb4D5 VH required 32 amino acid changes, which were
`installed with a 361-mer containing 59 mismatches to the
`mumAb4D5 template. Two of eight clones sequenced precisely
`encode humAb4D5-5, although one of these clones contained a
`single nucleotide imperfection. The six other clones were es-
`sentially humanized but contained a small number of errors: <3
`nucleotide changes and <1 single nucleotide deletion per kilo-
`base. Additional humanized variants (Table 1) were constructed
`by site-directed mutagenesis of humAb4D5-5.
`Expression levels of humAb4D5 variants were 7—15 ug/ml
`as judged by ELISA using immobilized p185“Rz ECD.
`Successive harvests of five 10-cm plates allowed 200—500 ug
`of each variant to be produced in a week. Antibodies affinity
`purified on protein A gave a single band on a Coomassie
`blue-stained SDS/polyacrylamide gel of mobility consistent
`with the expected mass of 2150 kDa. Electrophoresis under
`reducing conditions gave two bands consistent with the
`expected mass of free heavy (48 kDa) and light (23 kDa)
`chains (data not shown). N-terminal sequence analysis (10
`cycles) gave the mixed sequence expected (see Fig. 1) from
`an equimolar combination of light and heavy chains.
`humAb4D5 Variants. In general, FR residues were chosen
`from consensus human sequences (26) and CDR residues
`were chosen from mumAb4D5. Additional variants were
`constructed by replacing selected human residues in
`humAb4D5-1 with their mumAb4D5 counterparts. These are
`VH residues 71, 73, 78, 93, plus 102 and VL residues 55 plus
`66. VH residue 71 has previously been proposed by others
`(24) to be critical to the conformation of VH—CDRZ. Amino
`acid sequence differences between humAb4D5 variant mol-
`ecules are shown in Table 1 together with their pISSHEm ECD
`
`Table 1.
`
`mAb4D5
`variant
`humAb4D5-1
`humAb4D5-2
`humAb4D5-3
`humAb4D5—4
`humAb4D5-5
`humAb4D5-6
`humAb4D5-7
`humAb4D5-8
`humAb4D5
`
`71
`(FR3)
`R
`Ala
`Ala
`Ala
`Ala
`Ala
`Ala
`Ala
`Ala
`
`73
`(FR3)
`D
`D
`Thr
`Thr
`Thr
`Thr
`Thr
`Thr
`Thr
`
`plSSHER2 ECD binding affinity and anti-proliferative activities of mAb4D5 variants
`VH residue
`VL residue
`78
`(FR3)
`L
`L
`Ala
`L
`Ala
`Ala
`Ala
`Ala
`Ala
`
`93
`(FR3)
`A
`A
`Ser
`Ser
`Ser
`Ser
`Ser
`Ser
`Ser
`
`102
`(CDR3)
`V
`V
`V
`V
`V
`V
`Tyr
`Tyr
`Tyr
`
`55
`(CDR2)
`E
`E
`E
`E
`E
`Tyr
`E
`Tyr
`Tyr
`
`66
`(FR3)
`G
`G
`G
`Arg
`Arg
`Arg
`Arg
`Arg
`Arg
`
`.
`
`Kd,
`nM
`25
`4.7
`4.4
`0.82
`1. 1
`0.22
`0.62
`0.10
`0.30
`
`Relative cell
`proliferation
`102
`101
`66
`56
`48
`51
`53
`54
`37
`
`Human and murine residues are shown in one-letter and three-letter amino acid codes, respectively. Kd values for the p185HERZ ECD were
`determined by the method of Friguet et al. (41) and the standard error of each estimate is :10%. Proliferation of SK-BR-3 cells incubated for
`96 hr with mAb4D5 variants is shown as a percentage of the untreated control as described (7). Data represent the maximal antiproliferative
`effect for each variant (see Fig. 2) calculated as the mean of triplicate determinations at a mAb4D5 concentration of 8 ug/ml. Data are all taken
`from the same experiment and the estimated standard error is t15%.
`
`

`

`4288
`
`100
`
`00O
`
`aO
`
`Percentofcontrolcell
`proliferatron
`
`Immunology: Carter et a1.
`
`
`huMAb4D5-1
`
`
`
`
`
`
`huMAb4D5-8
`
`Proc. Natl. Acad. Sci. USA 89 (1992)
`
`placement ofR71 in humAb4D5-l with the corresponding murine
`residue, A71 (hurnAb4D5-2). In contrast, replacing VH L78 in
`humAb4D5-4 with the murine residue A78 (humAb4D5-5) does
`not significantly change the affinity for the p185HERZ ECD or
`change antiproliferative activity, suggesting that residue 78 is not
`of critical functional significance to humAb4D5 in interacting
`with p185HERZ ECD.
`VL residue 66 is usually a glycine in human and murine
`K-chain sequences (26) but an arginine occupies this position
`in the mumAb4D5 K light chain. The side chain of residue 66
`is likely to affect the conformation of VL—CDRl and VL—
`CDR2 and the hairpin turn at residues 68—69 (Fig. 3). Con-
`sistent with the importance of this residue, the mutation VL
`G66R (humAb4D5-3 —> humAb4D5-5) increases the affinity
`for the p18SHER2 ECD by 4—fold with a concomitant increase
`in antiproliferative activity.
`From molecular modeling, it appears that the side chain of
`mumAb4D5 VL Y55 may either stabilize the conformation of
`VH—CDR3 or provide an interaction at the VL—VH interface.
`The latter function may be dependent on the presence of VH
`Y102. In the context of humAb4D5-5 the mutations VL E55Y
`(humAb4D5-6) and V" V102Y (humAb4D5-7) individually
`increase the affinity for p185"ERZ ECD by 5-fold and 2-fold,
`respectively, whereas together (humAb4D5-8) they increase
`the affinity by ll-fold. This is consistent with either proposed
`role of VL Y55 and V" Y102.
`Secondary Immune Function of humAMDS-s. humAb4D5-8
`efficiently mediates ADCC against SK-BR-3 breast carcinoma
`cells, which overexpress p185HERZ at high levels as anticipated
`from its IgGl isotype (Table 2). In contrast, humAb4D5—8 is
`very ineflicient in mediating ADCC against the normal lung
`epithelium cell line WI-38, which expresses p185""5"2 at 100-
`fold lower levels than SK—BR—3 cells (Table 2). The murine
`parent antibody is not very effective in mediating ADCC against
`either SK-BR—3 or WI-38 cells.
`
`DISCUSSION
`
`mumAb4D5 is potentially useful for human therapy since it is
`cytostatic toward human breast and ovarian tumor lines over-
`expressing plSSHERZ. Here we have humanized mumAb4D5 in
`an attempt to improve its potential clinical efficacy by reducing
`its immunogenicity and tailoring the Fc region to support ADCC
`and possibly CDC.
`Rapid humanization of humAb4D5 was facilitated by the
`gene conversion mutagenesis strategy developed here using
`long preassembled oligonucleotides. This method uses less
`
`4
`
`12
`8
`[MAb4D5 variant] ttg/ml
`
`16
`
`Inhibition of SK—BR-3 proliferation by mAb4D5 variants.
`FIG. 2.
`Relative cell proliferation was determined as described (7) and data
`(average of triplicate determinations) are presented as a percentage
`of results with untreated cultures for mumAb4D5, humAb4D5-8, and
`humAb4D5-1.
`
`binding affinity and maximal antiproliferative activities
`against SK-BR-3 cells. Very similar Kd values were obtained
`for binding mAb4D5 variants to either SK-BR—3 cells (GK.
`and N. Dua, unpublished data) or to pl8SHER2 ECD (Table 1).
`The most potent humanized variant designed by molecular
`modeling, humAb4D5-8, contains five FR residues from
`mumAb4D5. This antibody binds the p18SHER2 ECD 3-fold
`more tightly than does mumAb4D5 itself (Table l) and has
`comparable antiproliferative activity with SK-BR—3 cells
`(Fig. 2). In contrast, humAb4D5-1 is the most humanized but
`least potent mumAb4D5 variant, created by simply installing
`the mumAb4D5 CDRs into the consensus human sequences.
`humAb4D5-1 binds the p185HERZ ECD 80—fold less tightly
`than does the murine antibody and has no detectable antipro-
`liferative activity at the highest antibody concentration in-
`vestigated (16 pg/ml).
`The antiproliferative activity of humAb4D5 variants
`against p185HER2 overexpressing SK-BR-3 cells is not simply
`correlated with their binding affinity for the p185HERZ ECD-—
`e.g. , installation of three murine residues into the VH domain
`of humAb4D5-2 (D73T, L78A, and A938) to create
`humAb4D5-3 does not change the antigen binding affinity but
`does confer significant antiproliferative activity (Table 1).
`The importance of VH residue 71 (24) is supported by the
`observed 5-fold increase in affinity for p185HERZ ECD on re-
`
`
`
`FIG. 3. Stereoview of a-car-
`bon tracing for model of hum-
`Ab4DS-8 VL and V“. The CDR
`residues (26) are shown in boldface
`and side chains of VH residues
`A71, T73, A78, S93, and Y102 and
`VL residues Y55 and R66 (see Ta-
`ble 1) are shown.
`
`

`

`Immunology: Carter et al.
`
`Proc. Natl. Acad. Sci. USA 89 (1992)
`
`4289
`
`Table 2. Selectivity of ADCC mediated by mAb4D5 variants
`Efl‘ector/
`SK-BR-3
`WI-38
`target ——
`ratio
`mumAb4D5 humAb4D5-8 mumAb4D5 humAb4D5-8
`
`25:1
`12.5:1
`6.25:1
`3.13:1
`
`25:1
`12.521
`6.25:1
`3.13:1
`
`Antibody concentration, 100 ng/ml
`<1.0
`9.3
`7.5
`<1.0
`11.1
`4.7
`<1.0
`8.9
`0.9
`<1.0
`8.5
`4.6
`Antibody concentration, 10 ng/ml
`<1.0
`3.1
`6.1
`<1.0
`1.7
`5.5
`1.3
`2.2
`2.0
`<1.0
`0.8
`2.4
`
`40.6
`36.8
`35.2
`19.6
`
`33.4
`26.2
`21.0
`13.4
`
`Sensitivity to ADCC of human cell lines WI—38 (normal lung
`epithelium) and SK-BR-3 (breast tumor), which express 0.6 and 64
`pg of p185mam per pg of cell protein, respectively, as determined by
`ELISA (40). ADCC assays were carried out as described (15) using
`interleukin 2 activated human peripheral blood mononuclear cells as
`effector cells and either WI-38 or SK-BR—3 target cells in 96-well
`microtiter plates for 4 hr at 37°C at different antibody concentrations.
`Values given represent percentage specific cell lysis as determined
`by “Cr release. The estimated standard error in these quadruplicate
`determinations was :10%.
`
`than half the amount of synthetic DNA, as does total gene
`synthesis, and does not require convenient restriction sites in
`the target DNA. Our method appears to be simpler and more
`reliable than a similar protocol recently reported (42). Tran-
`sient expression of humAb4D5 in human embryonic kidney
`293 cells permitted the isolation of 0.2- to 0.5-mg humAb4D5
`variants for rapid characterization by growth inhibition and
`antigen binding affinity assays. Furthermore, different com-
`binations of light and heavy chain were readily tested by
`cotransfection of corresponding cDNA expression vectors.
`The crucial role of molecular modeling in the humanization
`of mumAb4D5 is illustrated by the designed variant
`humAb4D5-8, which binds the p185flERZ ECD 250-fold more
`tightly than the simple CDR loop swap variant humAb4D5-1.
`It has previously been shown that the antigen binding affinity
`of a humanized antibody can be increased by mutagenesis
`based on molecular modeling (17, 20). Here we have designed
`a humanized antibody that binds its antigen 3-fold more
`tightly than the parent antibody and is almost as potent in
`blocking the proliferation of SK-BR-3 cells. While this result
`is gratifying, assessment of the success of molecular model-
`ing must await the outcome of ongoing x-ray crystallographic
`structure determination.
`humAb4D5-8 also supports cytotoxicity via ADCC against
`SK-BR-3 tumor cells in the presence ofhuman effector cells but
`is not effective in directing the killing of normal (WI-38) cells,
`which express p185HERZ at much lower levels. This augurs well
`for the ongoing treatment of human cancers overexpressing
`p18SHER2 by using humAb4D5—8.
`
`We thank Bill Henzel for N-terminal sequence analysis of mAb4D5
`variants; Nancy Simpson for sequencing the cDNAs for mumAb4D5
`V-region genes; Maria Yang for providing the CL-containing clone;
`Susie Wong for performing amino acid composition analysis; Irene
`Figari for performing the ADCC assays; Mark Vasser, Parkash
`Jhurani, Peter Ng, and Leonie Meima for synthesizing oligonucleo—
`tides; Bob Kelley for helpful discussions; and Tony Kossiakoff for
`support.
`
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