How to run grep with while loop in shell script?

Question

I'm trying to make shell script that counts 9 letters words consisted of A, G, C, T in B.txt.

First, 9bp_cases.txt contains

AAAAAAAAA
AAAAAAAAG
AAAAAAAAC
AAAAAAAAT
AAAAAAAGA
AAAAAAAGG
AAAAAAAGC
...

//#!/bin/bash

file=/Dataset/4.synTF/2.Sequence/9bp_cases.txt

# CSV 파일이 존재하지 않으면 종료

if [ ! -f "$file" ]; then
    echo "CSV 파일이 존재하지 않습니다: $file" >&2
    exit 1 
fi

cat 9bp_cases.txt | while read line;
do
    echo $line 
    grep -i -o $line B.txt | wc -w
done 

The result is like this:

//AAAAAAAAA
0
AAAAAAAAG
0
AAAAAAAAC
0
AAAAAAAAT
0
AAAAAAAGA
0

None of the words is counted correctly. However, when I run the simple code, it returns result well.

grep -i -o AAAAAAAA B.txt | wc -w
33410

I guess $line after grep is not recognized by the command grep. Can you please help me?

Thank you.